There's another service in the same space ... PayBitBack.
Simply mention a person in a Tweet and then also mentioni @PayBitBack and the service will reply with a bitcoin address for the tip jar. The funds received into the tip jar can then be redeemed only by that person. http://www.PayBitBack.com
I've tried it ... and it worked fine when the recipient understands bitcoin. For others, it didn't go as well. I doubt the tip I sent to a photographer ever got redeemed.
YouTipIt has "escrowed TipIts" which work the same way -- you initiate a tip to any Facebook user -- and only that user can redeem the tip.