A lot of comments here seem to focus on how to use it to replace payments for an industry (like music) or to replace the subscription model for a webapp, and maybe that is a bit far-fetched but I can see a huge use in this for low-level stuff.

If I Google a programming exception and get an answer from a blog I can show them some love. I create a lot of small websites used by friends and people from school or some other social context and I can very well see myself sticking that button on all of them to help me buy an extra beer this weekend.

If it grows enough it might be able to fund some "real" stuff, but I don't think it should be put in that context from the get-go.