I was reading a magazine recently and it made the sensible comment that you should try to keep the chain running straight. That is, don't select gears where the chain is on, say, the inner chain ring while it's running on the outer rear cog. Chains are quite flexible so is it the chain they are more concerned about, or possibly the potential damage it might do to the gear teeth? I ask this because on my Cannondale road bike, I have 2 up front and 7 behind and some of the rear cog teeth look a little rounder than normal. Is that because I've been inadvertently running the chain on the 'wrong' gear selections? The gear ratios are such that I don't have too many duplicated, so they are mostly 'valid' selections as it were.