I downloaded a free trial version of Breeze System's photo booth software for DSLRs and hooked my Canon 7d up to the computer via USB. I was going to have the live view on one monitor and the snapped photo on the other. I even bought a remote control for my camera so guests wouldn't have to run back and forth to take photos. A good flash is nice to have. I'm using my Canon 580EX II Speedlite which is *awesome*. It's turns most of my photos to gold, I tell ya.
Unfortunately I couldn't figure out how to keep the camera from running out of batteries since it wouldn't go into sleep mode while connected to the computer. I also wanted to use it to take photos of the housewarming party (which I ended up being WAY too busy to do, though I did manage to get some food photos).
For more information on setting up a photo booth, this tutorial was very helpful
Despite my failures, we were able to do some testing :)