I've got an original set of Avid mechanical discs [essentially BB7s] that are over 6 years old and going strong. I also have a new set that are performing well. The BB7 is my go to brake if I want to run discs.
BTW - I stared a
Big Dummy/Surly Xtracycle Google Group if any BD owners want to join and talk about how they are building/setting up and using their BDs.