Wifi problems Mac OS X 10.8.2 MacBook Pro
If this is in your home, do you have an older microwave oven nearby? Or a 2.4GHz cordless phone? Baby monitor? Anything else "wireless" (that's not a wireless router/access point)?

Have you tried changing the channel of the wireless on the router? Many newer routers will do a "site survey" and indicate an unused wireless channel.

I have had similar problems with wireless in the past and solved it by changing the wireless channel.