I just put some BB7s on my Stumpjumper hardtail today, to replace my horrifble v-brakes.
I never expected disc brakes to be such an upgrade. These things really kick ass. I like how when I pull the levers, my bike stops.
The auto-centering feature on the rear caliper didn't work too well though, and it took me and another guy damn near half an hour to get the thing positioned properly. But once it's dialed in, it's great. The pad adjusters are brilliant and easy to use.
I like these brakes a lot, they're a huge upgrade over regular v-brakes. They're not too expensive. They're kind of a ***** to install but that could well be operator error. Overall I'm happy with them!