I saw this problem a while back and I'm not sure whether I blogged it so here goes.
I bought a MacBook pro a while back because "Mac's just work" and the battery life is very good. Anyway, I was having problems connecting to the WiFi, the router would appear and disappear from the list and trying to connect caused all manner of errors and timeouts. I had a D-Link wireless router and despite these being the cheap cable company ones, they should be more than adequate, especially sitting across the room from the laptop. Anyway, the MacBook has a lot of metal on it and the antenna is alongside the screen so it's never going to be great. No doubt the Apple AirPort is cranked so that this issue is not so obvious and to give Apple staff a chance to sell you something you shouldn't need!
I called up Virgin Media and complained and they sent me a new router since the one I had was a good 3 or 4 years old and might have been dying. I had the same problem.
Fortunately, the new wireless router was supported by http://www.dd-wrt.com/site/index a free, open-source router firmware for many types of hardware. The thing that I was particularly taken with was the adjustable antenna power. I installed it and bumped up the power and all was again fine in MacBook land.
Anyway, I have just been upgraded to a Virgin Super Hub which is a cable modem and wireless router combined and which allows a 50Mb download. Not really thinking, I tried to get the MacBook to connect and had problems again, eventually remembering my previous problems. It seems even the new Super Hub is not powerful enough for a MacBook Pro. In the end, I plugged the other wireless router back in to the ethernet on the Super Hub so I have two wireless access points but at least I can connect the MacBook. I might disable the wireless on the new Hub. Seems daft but the local airwaves are already polluted with WiFi.