"I don't think I used the same password but both sites were the first I signed up to so I might have made that mistake"

I'm sorry to hear about your loss. I too have an MtGox account (with BTC in it..) that I hope is restored to the pink of health in due course.

I suspect that the trouble here is using the same username/password on other sites. It seems reasonable to assume that if you have captured a username/password combination that one (bad person) would attempt to use the same credentials at similar sites - it's an easy fix.

Is there a way to report that wallet address as a potential "bad" one? Some form of reputation for addresses might help reduce the affect of stealing currency, even if slightly (every little helps!)...