Are you using self-extracting BB bolts? The only time I had a problem with cranks coming loose was when I was using those - being paranoid about messing up a pair of nice cranks, I didn't tighten the hex bolt enough and they came off in the middle of an alleycat (whoops). And it's typically the non-drive side that works itself loose. And actually, I think the only way that you can deform the cranks is by overtightening them (since you're pushing the crank beyond the taper on the spindle and smushing the aluminum), so if you got them new and didn't tighten them enough, you're probably fine.