*edit* Also.. any reason why people would advise against using blockchain wallet ?
It's all about trust, you are trusting someone (know their name? address? anything but nick?) to hold your bitcoins securely.
and after the linode incident if they are on a vps you are trusting their host to an extent too
if you must use these online wallets keep a minimum balance there and use a secure wallet you have control over for the bulk of your funds
That seems a little unfair; there is a certain amount of trust to using blockchain; but they are a special case of online wallet. All the work with the secrets is done by javascript running on your browser. blockchain.info itself only stores an encrypted block of data that your browser decrypts with the password.
The trust is that their software hasn't been compromised; but other than that you aren't trusting that they hold your bitcoins securely -- if their database was published for all to see, it's unlikely any coins could be stolen.