I'm in the Southern California/Los Angeles metro area. I haven't found a lower temp limit yet. The temps can get down a little below freezing here in December/January (this morning its about 32F/0C), but that can be mitigated with a few extra layers of clothing. It DOES freak out my co-workers when I come rolling up to the building on a bicycle in that type of weather.

FWIW: I hate riding in the rain, just won't do it.