Interesting article. I can't help wondering whether this kind of theft would even be punishable by law; good luck explaining to a judge what exactly has been stolen. Technically, the result of the theft is just an alteration of the Blockchain, which is public by design.
Well, it seems that there is money to make, and here is the proof that some people are already on it...
This also demonstrate that you can use a service like Brainwallet, but you need to choose a really strong passphrase, that will resist bruteforce. If any computer or any other human can think of it, you are doomed !