I've finally put down the money to buy a quality knife and it's sharpness is amazing!
How do I take care of it so that the edge lasts and the knife stays sharp?
Always use a cutting surface made for a knife, particularly a wooden chopping board/block. Avoid contact with hard surfaces such as metal, glass, or stone; these will quickly cause dulling or even chipping of most knives. Also avoid cutting frozen items, for the same reason.
Use the dull end ("top") of the knife for scraping food off surfaces, or use a scraper or spatula instead. Knives are meant to cut straight, along the edge; scraping one sideways across any surface will misalign the edge very quickly.
Do not use more force than necessary. A sharp knife should cut with very little effort. The more pressure you apply, the faster it will dull.
Use a cleaver for bones or other very hard foods. General-purpose chef's knives or smaller knives aren't appropriate for this task, and may chip or even snap.
Wash or rinse knives promptly after use. The moisture in many foods can be acidic and/or corrosive to the metal (fruits, onions, etc.).
Dry knives immediately with a soft cloth or towel. Stainless steel is resistant to rust and corrosion but not immune. This goes for all metal but especially knives, because even an imperceptible amount of rust along the edge will drastically hinder its ability to cut. Air-drying may also leave you with stains or "spots" due to salts and other trace minerals in the water.
Store knives in a dry, open area, away from other objects, to avoid moisture build-up, impacts, and secondary rust.
Do not put a knife in the dishwasher. A knife in a dishwasher is subject to impacts, corrosion, and warping of the wooden handle/joint. Quality knives should be hand-washed.
Honing a knife is a good way to restore a slightly dull knife. You will need an honing steel (sometimes misleadingly referred to as a sharpening steel), which can be bought inexpensively. Note that there are differences between steels; the best value tends to be in the $30 (USD) range.
Honing is not the same as sharpening. Honing helps to align the existing edge, which becomes skewed or "curled" after regular use. It will not help to create a new edge if the knife is damaged, e.g. if it is corroded or chipped due to not following the "General Care" advice above.
To hone a knife:
Here is a video illustrating the technique.
Knife sharpening involves a whetstone (AKA sharpening stone) and is an art unto itself. Some knife manufacturers do explain the process, however, the technique takes a long time to master and most home cooks will prefer to leave this to a professional.
If you find that regular honing is no longer effective at maintaining a knife's edge - and if it's been well-maintained, this should take several weeks or months - then it's time to get the knife sharpened.
An alternative to professional sharpening (or learning to use a whetstone) is to use a good-quality motorized electric sharpener, such as the Chef's Choice. This will obviously not yield the same result as a professional sharpening, but it is very convenient and fast.
Some people believe that all electric sharpeners will damage your knives. This may still be true of the cheaper, single-stage sharpeners, because they do a lot of grinding and generate a lot of heat. However, the more modern, higher-end sharpeners operate very quickly, have precise angle control, and use multiple stages mimicking the manual process (grinding, steeling, stropping).
The "grinding" stage on a multi-stage sharpener should only be used if the knife is already badly damaged, and will actually create a new edge. If your knife is in reasonable shape, then it's fine to use a good sharpener on a semi-regular basis as long as you don't grind too much. (Honing should still be your primary form of maintenance).
Yet another option, if you're on a tight budget, is to use sandpaper. Follow the link for additional information on technique, grit, and tutorials.
Yes, I LOVE my knives. Only have three plus a parer.
Get them professionally sharpened regularly, there is no substitute for that.
Hone them every time before you use them, don't cut on a hard surface (such as a marble or the like)
Some knives like the Wusthof knives I have will lose their sharpness quite quickly other's like Global are meant to keep it for a bit longer, so different knives mean different levels of TLC.
Additionally as others said, its important to keep your knives dry and not chuck them in the dish washer.
Alton Brown had a show covering this, I think the tutorial is online.
There's a difference between sharpening and honing your knifes. If your knives need sharpening, you should take it to a professional. After a few years of moderate use, it's probably time. Michael has a good suggestion, but only if you plan on sharpening your knives often enough to make it worth it. For regular maintenance, you want to use a honing steel on your knives, which will straighten out any place where the edge has "rolled". This does not actually "sharpen" the knife, as the sharpening process removes steel to create a new edge.
There is some difference between honing steels. In my own research a little while back, I decided they fell into about 3 basic types:
You can also get a ceramic honing rod, which would add an even finer finish, which you could use in addition to a regular honing steel.
One of the very best investments I've ever made in a kitchen tool is this Chefs Choice knife sharpener. It is motorized and has three levels of wheel - one for grinding out really bad knicks, one for sort of once-a-month resharpening and one for everyday honing that will leave your blade razor sharp. The angle guides make it nearly impossible to use wrong.
Now I've got nothing against learning to use a whetstone or waterstone - I know how from woodworking. And I'm all for you learning how to use a steel. But realistically, most home cooks aren't going to do either of these things. A good, motorized sharpener that produces excellent results in seconds is the perfect solution.
Here's a video on how to hone your knife, just as Mike explains it:
The honing keeps your knife sharp from day-to-day. But over time a dullness still accumulates that can't be fixed with honing. So you should have your knifes professionally sharpened from time to time (maybe once or twice a ear).
I have a $40 electric knife sharpener. It has two slots (for two stages of sharpening) with a rotating wheel inside. The slot's edges will guide the knife at the right angle.
It requires very little technique and effort, it's quick to learn and quick to use regularly.
It works marvel with the cheap knife set that I got years ago and I haven't had a need to buy another knife ever since.
Check if that would work on your quality knife (it may not). If it does, I recommend that.
If you don't want to learn how to use a whetstone or a waterstone and do want to be able to sharpen your knife at home, you can get a fairly inexpensive sharpener made by Henkels for your knife. Another option is to take it into a local store that does sharpening or ask your butcher where he gets his knives sharpened and have a professional do it.
Rust is the major enemy of a sharp anything, knife, razor, chisel. When you watch a sushi chef cut, the 1st action after cutting is wiping the blade off with a clean dry towel. Everytime! Keep your knives clean & dry and don't abuse the cutting edge. Protect them, they aren't can openers, scrapers, spatulas. My knives last 2 to 3 months between sharpening and I can easily cut paper thin slices of tomato if need be, Slicing newsprint is an accepted test of sharpness.
Electric knife sharpeners will literally eat your knife down, they remove a huge amount of material every time you use it. I've taught myself how to sharpen my knives using several grits of a natural water stone. (google how to sharpen with a Japanese water stone) Years ago, I used a sharpening guild and a 500/1000 grit combination manufactured water stone. Now I rarely use 500 unless the knife has been damaged. Mostly I start with 1000, then polish with 2000. It takes me 10 to 15 minutes per knife. When I can use a 4000 grit water stone, I may finally buy a really good Japanese Damascus made knife.
Japanese knives are different from European knives. The amount of carbon contained in the steel will determine how hard it is. Very good Japanese knives have extremely high carbon content. They are the sharpest knives in the world. The technique for sharpening European or Japanese knives also varies. High-quality hand-made Japanese knives made with Damascus layered steel can run thousands! A moderately priced one is 2-300. You can get decent Japanese knives for 100-200. This may seem high, but remember, this is a knife you purchase once in a lifetime. My grandson will get my knives when it's time.