In summation this week...
1.) Don't use the same password on a bunch of places
2.) Don't trade a decentralized currency in one central place
3.) Don't leave a pile of cash or BTC in an account at a website that everybody uses, but nobody really knows anything about
4.) Don't put 25,000 BTC in one wallet
5.) If you walk into a room full of cocks with a lubed up ass, consider the possibility you may get fucked.
Too many people here can tell you every technical detail about a block chain, and read transactions, but do the stupidest, common-sense-avoidable shit, and throw a tantrum.
If somebody lost 400k BTC in one transaction, in my mind, it's Satoshi or Mt. Gox's main account. There are probably people behind the scenes working on this now, and when the market opens, there is blood in the water, and there will be sharks. Don't sell your fucking bitcoins. Seriously. You're going to lose your ass. Wait a couple of weeks for all the drama to die down. Or sell them all, and we will buy them all up. But don't come in here crying a week from now saying you wish you'd held on to it.
There are very very few people here, all with small BTC amounts, claiming to have their Mt. Gox funds stolen. Whomever those 400k belonged to, they are who is going to take the hit. Mt. Gox will more than likely go out of business because of this, as they probably should.
Somebody should have noticed these vulnerabilities before it was compromised. People also need to keep in mind that a key feature of this whole thing is that the transactions are designed to not be reversible. Obviously this is a special case, but in general, if you have a lot of $BTC lying around someplace stupid, you should keep in mind if you lose it, that it is GONE. If it's a significant, or complete, chunk of your portfolio, you shouldn't leave it lying around on the equivalent of a park bench.