Personally, I just CRAVE steep steep downhills where your on the edge of losing your rear traction. I was on this hill, where I discovered my passion (pics will be up in a few days sorry), although it wasn't THAT steep, it was as fast as hell! That stuff really gets me pumping harder for the rest of the ride.
PS: Hardtails are so awesome on stairs. Man, when I went down a big set of stairs, my rear felt like it was going on a smooth downhill while my front was mr. rough-e-o.