This is a generally awesome tool.  In addition to it's other uses, it will allow us to keep Mybitcoin.com and it's (presumedly less honest) future competitors from the temptation of fractional reserve nonsense.  Just the threat that any Joe can run his addresses past block explorer and tell if his funds have been mixed with other accounts not his own, or otherwise borrowed without consent, should be enough to keep most on the up-and-up.  Not that I don't have a fair trust of Mybitcoin.com, I do have an account that has been climbing in value as of late, but I also feel better knowing that I can check on my balances without having to trust the websites' honesty itself.