SFO-HKG can be a difficult flight to upgrade on. There are many posts about this. On 2/10 the flight went out full in C and I know of at least one passenger who didn't clear the waitlist. On 2/11 it was again full in C. Don't know whether everyone cleared, but I didn't clear til 3 days out. On the otherhand it can get really bad....in September 2003 on the same flight (ehh UA 805) I didn't clear til 20 minutes prior and I was told there were at least 25 people who didn't clear. As ozstamps said it's a good idea to lock in some nice Y seats in case your upgrade doesn't clear.