The idea that I could donate money which the publisher hasn't agreed to receive and you could end up keeping it if the publisher doesn't decide they want to be a part of your service rubs me the wrong way.
Telling web publishers they have tips waiting for them is tricky business, i.e. Don't want to be spammy. We hope to develop some interesting ways to notify people that they have tips; but tippers have been filling this void by mentionig on services like Twitter that they've tipped someone for something.
For now, if a tip goes unclaimed by the publisher for 6 months, it's automatically canceled, and the money is returned to the tipper for them to use to tip something else.
We don't currently have a way for someone to block or decline tips for a particular website, but we've talked about adding this type of feature; someone could claim their site, then say they don't accept tips there.
Bottom line, we don't have any intentions of keeping people's money that goes unclaimed, we rather return it so they could fund other tips with it. People can also help support our operations by tipping us, TipTheWeb; eating our own dog food.
I don't know that I agree with the refund strategy as the way to handle the issue but it's good to hear you guys come down in a good place ethically/morally on the issue (as you say, the most important thing with this sort of site is trust).