Well... blockchain.info's wallet DOES sign transactions in the browser, as well as encrypt/decrypt the wallet in the browser, so that blockchain.info doesn't have access to your funds. This is pretty much a bitcoin client in your browser, that's almost (or in some cases more) as secure as the official client.
This pretty much makes bitcoin able to be used purely from your web browser, the only thing it lacks is the ability to run as its own node, instead it forwards your transactions after signing them in the browser, to blockchain.info's own bitcoin daemon, which then releases it to the rest of the network.
It would be interesting if the bitcoin daemon part could be made easy enough that any one could run it. Easily. Or if Blockchain would sell their service as a package to others.
