I, like most people, prefer fish to be cooked correctly. For salmon, this means soft and velvety (but warm) in the center -- what I would characterize as medium rare.
I consistently overcook for two reasons: one, fear of bad stuff and two, because I am guessing. What are good rules of thumb for telling when it's medium rare?
Press the salmon. The less cooked it is, the softer it will be. You more or less just have to learn by touch.
Broad rule of thumb: 6oz (flat-ish) portions of salmon take about three minutes to sear one side in a hot pan, flip, throw in a 350 oven for 5-6 minutes.
If roasting from raw, should be 11-13 minutes in a 350 oven.
There are no good rules of thumb for meat/fish doneness. There are acceptable ones which function almost always when the cook is experienced, and there are terrible ones (including the popular X minutes per centimeter thickness).
Buy a thermometer (you can find a decent one for the price of two kilos of salmon) and stick it into the thickest part of the fish. Wait until it shows 50°C. Stop the cooking process.
And while you are at it, use it for all other meats too (but at the proper temperatures, almost everything needs more than salmon).
If you fry filets in a pan, simply turn it when the "done color" reaches half way up on the side of the filet. Repeat on the other side. When it's just about done on the outside like this, the center is slightly rarer and in my opinion perfectly cooked.
