would it be possible or useful to back up everyones wallet somehow in an encrypted form in the block chain such that it would always be an up to date backup and also accessible from anywhere running bitcoin. you would be forced to use a strong password/phrase somehow.

maybe a completely stupid idea. just seems appealing that you could go to any computer with bitcoin on it, enter you're passphrase and voila, you have access to your wallet.  actually just writing this now thinking that this would be pretty stupid as there could be all sorts of spyware/key loggers on an unknown computer.