It's the N1. I don't think Google has or will talk about the N1 wifi issue but there are plenty of folks with the problem themselves who have been trying to figure out this issue since the phone became available.
Some have pretty much narrowed it down to a bug in the N1's wifi stack
Whether your affected or not with this bug seems to be a crap shoot with the N1 you received. Check to see if your N1's MAC address starts with a "38" instead of "00". N1's that start with a 38 seems to be prone to this issue, ie, mine. Whether you tried the compatible router fix, the static IP fix, the Wifi-Fixer app or whatever else 'fix' that were suggested, it just doesn't seem to work for everybody. Even this 2.2.1 update doesn't seem to be working for all
I have read numerous threads on this subject and I can't find them all but here's one thats 10 months old talking about this very issue. You'll come close to pulling your hair out reading some of these wifi issue threads!
WiFi constantly drops, won't stay connected when in sleep (option to never sleep IS selected) and won't reconnect - Android Help