I've got similar problems. I got my MacBook Pro in March, and it's worked fine up until the last month. Now, the wireless will drop out on occasion while I'm at home, often if I've been out and connected to another network before re-connecting to the home network. Also, once I've lost connectivity, when I switch AirPort off/on/off (usually it goes a few times), even while it's Off the bars are still searching, and although the home network's showing as connected, the browsers are offline.
At first I didn't think much of it and restarted the wireless from the router, then restarted AirPort, which seemed to fix it. But I've realised that the other 2 laptops using the network aren't affected by these 'drops'. I'm in a studio apartment, so I'm always in the same room as the router.
Starting to contact Mac help, but from what it looks like here, I might be searching for answers for awhile....