We went to Sturgis 2009 and arrived the last weekend of bike week, when everyone was leaving. Never needed a reservation anywhere, and all the prices were back down to normal (not to mention we missed the hailstorm). Went to Mt. Rushmore - be sure to check out all the tourist roads to get there - awesome riding.
We stayed in Hill City, nice cabin and just a hop and skip from Mt. Rushmore and Crazy Horse. highly recommend it. wish I could go this year, but the knee replacment comes first this time, even though I don't want it.