ChainTight Security has introduced ChainLock, a product that allows users to lock all or part of an online account using a bitcoin address.
An account is locked by transferring a small amount of bitcoin into the address, and the account is unlocked by transferring bitcoin out of the address.
A user can check the status of their account (locked/unlocked) simply by checking the balance of their bitcoin address without needing to log into their account.
There are also several enhanced features that ensure the security of a user's online account.
You can view tutorial videos of ChainLock here:
http://chaintightsecurity.com/content
Imagine how much bitcoin will explode if used not just as a store of value (digital gold)... not just a currency... but also an authentication protocol for all of the banks, equity markets, exchanges, etc. As people engage bitcoin as an authentication protocol, they will begin to understand ALL of the benefits of bitcoin.