Based on some of the discussion here it seems like, in general there is some amount of difficulty in getting the tension of the timing belt or chain consistent throughout a full crank rotation. It seems that many of us that use belts (and maybe chains, too) have discovered that it's okay to run them at a little lower tension to avoid the problem of them being over tensioned at certain angles and that there appears to be no ill affect in doing it that way.
I used the Gates app and strumming the belt, but as I approached the correct frequency I noticed the timing cranks got harder to turn and nearly didn't spin at all when I gave them a good push. Lowering the tension a bit, but not enough to have the belt come off the cogs, allowed the cranks to spin a lot longer.
If it is the varying belt tension that's eating up bottom brackets, maybe just run them a little looser? I don't know. I would bet that the bearing in this Comotion are original from 2006. In any case, we've probably put another 6-8,000 miles on it (at least 3000 since we put the belt on) and they seem to still be good. Maybe I should pull out my dial indicator and check if I'm on the ball or not.