He lost 10,000 BTC in the MyBitcoin scandal. From now on he's going to use the standard client, and encrypt the wallet.dat with truecrypt, and back it up on Dropbox. And he's looking into deterministic private keys. That might be the safest way to save his horde.
I would not store wallet.dat in Dropbox:
http://venturebeat.com/2011/06/21/dropbox-files-left-unprotected-for-four-hours-due-to-software-bug/I would definitely call that a big "Whoops", considering people ARE using it to store things like financial data, legal forms, and more. Dropbox is GREAT for file sharing, but I would never place anything sensitive there.