How to reclaim unclaimed Bitcoins sent via Blockchain.info to Facebook/Email friends? The FAQ says

What happens if the transaction is not claimed?

The private key the funds were sent to is saved in the senders archived addresses. The sender can reclaim the amount at anytime by sweeping that address, it's up to you how long you wait for the amount to be claimed. The address will be labeled "username (Sent Via XX)"

How is this done specifically?
Under Receive Money, Archived, find the address in question ("username (Sent Via XX"). Click this button to bring it back to active addresses:


Under Send Money, Custom, send all the money from that address to another address in your wallet. You can now archive the address again.