I forgot one thing. Never buy a knife you haven't held in your hand. Everyone's hands are different and different knives have different weights and shapes. By the way, most quality knives have a lifetime guarantee.
IMO, this is the most important thing-- feel. I happen to like my Henkels Four Star chef's knife, and I've been using the same knife for the past 15 years. It feels natural for me. My GF doesn't like it, and prefers a different knife. I can use hers if I need to, but it feels less natural for me and slows me down.
Oh, and one other thing-- keep it sharp. The steel that comes with knife sets is mostly useless (and not used to sharpen), and a lot of the so-called "professionals" are less than great at sharpening. I've taken some cooking classes, and the chefs have experienced this-- so-called "pros" who would leave hollows in the blade, sharpen at the wrong angle, even de-temper the metal. Find someone that knows what they are doing to protect your investment.
As far as home sharpeners, one of the chefs recommended the Furi Ozitech Diamond Fingers sharpener (says he hasn't used a professional in five years). Another recommended using good old oil stones. In either case, most say to stay away from electrical-powered sharpeners, since they can chew off quite a bit of metal... you might get a good edge, but the knife won't last as long.