Mine is sitting at: Service Pack Installation 1 out of 3: 5% for a long time now after the first restart.... :S
EDIT: Phew, it was at 5% for like 45 minutes, then more or less blazed through the rest. Total time for the install was almost an hour, including the download. Everything seems to be working more or less OK.
EDIT2: Took at least 3x less time on my laptop with 32bit Home Premium.