I'd always wondered. The blocks usually seemed designed to have the knives go in blade down, so that the blade touched wood coming in and out. But I know that when I whittle, cutting the wood wears the blade of a knife down very, very quickly. I'd always wondered if that regular contact with the wood from sliding into and out of the blocks could be wearing my knives down. Does it? If so, does putting them in blade up (against the design of the block - it would seem) do any better for them?
Wooden blocks are ideal for knife storage because they keep the blades dry (the wood absorbs some of the humidity in the air), preventing rusting.
The motion of inserting and withdrawing blades over wood will not noticeably dull them, because you're not actually cutting the wood or indeed even applying any pressure as you do so.
A good tip is to use a good quality steel to sharpen your knives with just one or two passes on each side before each use. Wash them with hot water by hand, avoiding dishwashers unless you like replacing your knives annually, then return them to the block once they're fully dried.
Technically, yes. While wood is a preferable surface to many others for drawing your blade across it will still cause wear. If you're using a block, the slots should be horizontal.
Your knife block is poorly designed. I have a Shun knife block, the blades go in sideways. I just searched for J.A. Henckels and Wusthof blocks on Amazon as well, all horizontal.
Is this worth buying a new block over? Probably not, as the other answers in this thread indicate, it's not that big of a deal. It is less than ideal however.
We have two knife blocks. One has vertical holes, the other has horizontal holes. The horizontal block gives us all the advantages of wood, without the big disadvantage you just pointed out. The cutting edges don't rest against wood all the time, and are less likely to be in contact with said wood when being placed/removed.
I'm not a whittler, but I think that what causes the blade to wear is pulling it across the wood. The blade should be fine as long as it is drawn lengthwise (like you are cutting something in half). Blades are very strong this way, but since the edge is very thin, it can easily be bent by having things pull across it.
Since wood is much softer than metal, I suspect there would be very little impact on the integrity of the blade. It it were pushed very hard into the wood, it might bend, but under normal use, I can't see any problems.
It's much better to put the knife in a wooden block than to put it in a drawer and have it rattle around with other metallic objects. Most pro knife sets come with a wooden block so I would assume that is the preferred storage method.
If you are concerned that pulling the knives out along the wood will dull the blade than as you pull out, also pull away from the blade side so the knife blade doesn't rub against the wood.
As Chris Cudmore stated, actual use of the knife on a wood cutting board will dull the blade far more. My guess would be that one average knife use dulls as much as 100's of in and outs of the block. And if you carefully pull the knife out and replace it so the edge does not even slide on the wood (as I do), then no block damage at all.