i took the 15 day one, spread out over couple months. It was useful. Again, depends on the instructors. I didn't think Harris was that great. We had Lyonell for path, and the dude was amazing--definately right up with goljan. Infact, a lot of hsi stuff was presented in a similar fashion. I thought kudrath was pretty good too. Turco for biochem was very much amazing as well. Most of these guys are good.
The usefulness of the class depends on whether u learn by listening or reading on your own. I am much better on my own, but I took a spread out one, so it was more helpful, in terms of the way I learn. Overall, it was still useful.