Go get your reservation. Even if you think you have a 10% chance of going to SIGGRAPH 2011 this year, I recommend holding a room now. You can cancel the reservation later at no cost until July 21.
Me, I went with the Empire Landmark Hotel, as it was a good balance between price and distance (location also sounded good). The YWCA was very tempting, though – really, if you’re traveling alone (I’m with 2 others), it’s an incredible bargain ($99 a night) for a single person and has a noticeably higher rating than the Empire Landmark on TripAdvisor.
Oh, also, if you’re an interactive rendering type of person, don’t forget that HPG 2011 is colocated with SIGGRAPH 2011 and starts on August 5 (a Friday), so you might want to book from August 4th on. You can always carve off days from your reservation later. That said, choosing August 4th does trim down the available hotels a bit. For me, HPG is a must-attend; when it was colocated with SIGGRAPH in 2009 (it alternates between SIGGRAPH in North America and EGSR in Europe) I found it offered more relevant papers than all of SIGGRAPH itself.