We haven't seen this with my iPhone 3G and the 2.2.1 firmware, but apparently some users lost wi-fi connectivity after applying that firmware update.
The problem seems to affect iPhones and older iPhone 3Gs, and it seems to be heat-related, as some users say putting the affected iPhone into the freezer
for a short time temporarily
The obvious assumption is overheating, and some believe that what happened was Apple was throttling the wi-fi chip until 2.2.1 and that after removing that "brake," older units were affected by overheating.
Interestingly, Apple tells users affected by the issue to request a unit
that does not have 2.2.1 when calling. Admission of an issue in the 2.2.1 firmware, but no patch to fix it apparently?
Typical of Apple, there's no official word on the issue. If you have an issue, it seems like tech support is understanding enough, but an admission of an actual problem would be a nice (although unexpected, from Apple) thing.