Wallet security seems like one of the more major problems for the general population to use BitCoins, especially considering the unability to recover stolen BitCoins. It seems like Credit Card Fraud squared, if BitCoins were to become really popular.
Although, from a purely theoretical view (and one that most hardcore BitCoin users would oppose), it might be possible to create a central institute then, which could oversee which BitCoins are "legit" and which are reported "stolen".