I just finished my first full winter commuting by bike in NJ/NYC. I have BB7's, and the rear brake would freeze up below around 20F (-5C?). Not sure what I did - maybe got water into the mechanism while cleaning it (and I cleaned the bike regularly due to salt, etc.). Tried WD40 into the brake and chain lube, but the problem persisted. Didn't have the problem up front, though. Was thinking of going in the opposite direction and getting hydraulic brakes for next winter. Sounds like I need to be careful no matter what I do.