Rumor mill says it was an SQL injection attack that allowed the hacker to steal the user database. Protecting against an SQL injection attack on a website is fairly trivial which makes me doubt the ability and "security sense" of whomever developed that site.
To my knowledge they have not said if the database compromise lead to the hacked account. It seems very likely though, with access to the password hash weak passwords can be easily dictionary/bruteforced. Why anyone with 500k bitcoins would have a weak password leaves me guessing though. This is a lesson everyone can learn from though, if your password is not long, random, and mixed with letters, symbols and numbers you're at risk.
What is even more scary is it appears that the e-mail accounts on the list are now being attacked. If someone compromises your e-mail box your generally screwed as they can then reset passwords other websites with lax security like MTGOX.
It seems like there have been some artificial attempts to stabilize the market through the use of huge asks in order to drum up vendor adoption of bitcoin. I don't see how this can work, all you are going to do is scare away all the buyers. People buy bitcoins because they expect them to gain value, if you lock them to the dollar you might as well just keep your dollars.