My wireless also has some strange behaviors that look similar. Actually if somebody has some steps to get some debug info, I'd be happy. I've opened a bug on bugzilla but with very few info.
I use OS2007 latest, WEP, hadhoc channel 3 to an IPW2200 (HP laptop running debian).
Sometimes it works. Sometimes not
When it doesn't work, the device simply doesn't see any network, not only mine is not working.
And I use it at two different places, same problem. One place has maybe 8 networks, the other nothing (checked with kismet)
And also yep, it appeared after a while. When I received the device (2 months or so), I had no problem.

Looks like some kind of race condition.. if I ask my crystal ball.

I hope this is a bit better with OS2008.