I find your problems a bit puzzling. I certainly believe that both of you are experiencing less than stellar performance from you BB-7s, but we have had (road version) BB-7s on our tandem for nearly a year (~2000 miles). So far the only problems with them are that they sometimes squeek, especially when a little wet or dirty. When they start to squeek, 90% of the time it's the front brake. If I take off the front wheel, run an alcohol-soaked rag between the pads, everything is okay. Also on a hard turn, they will just barely rub a little, again I think it's the front, but no biggie.
As far as performance goes, they perform really well. I mean they can stop fast, and a tandem carries some pretty good momentum. The feel certainly isn't the same as with wheel rubbers, but once you get used to them, they will feel normal. Now, when I jump on my half bike, I find I have to put more beef into braking than with our tandem.
Bottom line; something isn't performing up to par. I wonder if Avid has changed their pad formulation. It's important that when you have problems like this, you clearly convey them to not only your LBS, but directly to Avid. That's how a manufacture learns and develops better products. If many are having the same problem, then it needs to be addressed or the product goes away, cause there's always someone coming with a better mouse trap.