Which means people can use this to pay each other. If I want to pay you $100 I can give $100 to a charity of your choice. You count that as a donation you're making, I count it as ordinary spending. If you look at my donations page you can see that I've done this a few times, accepting a donation in my name in place of payment.

(If this became popular you could have charities generate unique receipts, so that someone couldn't "pay" both Xavier and Yolanda with the same $Z donation to charity W, but so far I've only done this with people I trust not to rip me off.)

Update 2014-02-24: I still think this is a good idea, but I'm less enthusiastic about it than I was. The big problem is that it makes your actions less legible and harder to explain. If I say "I gave $X" that's clear, but if it's "I claim moral responsibility for donating $X, including $Y that I donated directly and $Z that other people gave on my behalf as a kind of payment" I need to explain a lot of background.

[1] In fact, if I could move money from my salary to my employer donation match I would. Money you donate to charity counts as if you hadn't earned it for federal income tax purposes, but there are lots of other taxes including state income tax, social security, etc, so if the money goes to charity without ever legally being yours that's better. Not that I fully understand taxes.