Originally posted by AC*SE:
2) Yes, you have to clear customs at SFO. After all, you are entering the USA. I am not sure whether there is sterile transit for baggage through the US--I am pretty sure there is not, which means you have to claim and clear your bag, then put it back to recheck.
I was offered transit facilities at SFO while travelling UA HKG-SFO-YYZ. I ended up entering the US for 4 hours, but my baggage went straight through to Toronto.