Hm, someone could set a sweatshop buying and selling small value stuff to build up reputation on addresses and then sell wallets containing anonymous highly reputable addresses to people that don't wanna build a good reputation but wanna have one anyway; depending on the scale of the operation and how big the clientbase is (and the percentage of them that will live up to the bought reputations or burn it down), this could be quite damaging to the web-of-trust reputation system...
I don't think anyone really bases reputation on bitcoin addresses. They usually tie it to an online identity. That way when you generate a new address or make a new wallet your reputation doesn't disappear!