The Home Theater blog has a good post on how-to wall mount a LCD or Plasma.
Wall mounts are kind of funny -- most every screen you see in ads and in commercial spaces are likely wall mounted in a very clean way, but when you get yours home you'll quickly realize how much of a pain it is to do and requires some real knowledge of construction and electrical techniques. A wall-mounted screen without hidden cabling is kind of an eyesore and I can't help but look at my TV over the fireplace and the jumble of wires below and wish I found someone to do a clean job on it. I tried a local electrician and they had never done one and couldn't really give a quote on what it might cost.
I figure with the ubiquity of cheap plasma and LCD screens, perhaps a cottage industry of installers will pop up to help people hide their TVs in the next few years.