I am now on my 2nd macbook (I had to return my first one on Sunday) and I am continuing to have the same problem. My macbook disconnects from the network after about 3 days of use, then will not reconnect. It sees the wireless network just dandy, but when I try to connect to it, it says 'network timed out'. And every other wireless device in the house (including my ipod touch) will happily connect and work just fine.
I've had Macbook #2 for 4 days, and it started the problem last night, and as of 10 minutes ago, absolutely refuses to connect. I'm posting this from my old pc laptop. I am so -angry- I'm... beyond words.
Calling Apple now, we'll see what happens. (It doesn't seem to matter if I'm on battery or plugged in, and I've rebooted several times, ran an OS update, turned off the airport then turned it back on.... I have years of PC troubleshooting experience).