I know there are a variety of ways to donate your laptop's unused processing power - this is the first I've seen asking for smartphone power. And for a great cause! You can help the Garvin Institute of Medical Research work on finding cures for breast, ovarian, prostate or pancreatic cancer.
According to the Garvin Institute, with "100,000 DreamLab apps working on smartphones, the team would be able to process data about 3,000 times faster than they are currently able, and with 5 million users, that rate would increase to 150,000 times." (source)
On the UX side, great that they let you specify data or wifi & set a limit on how much is used.
Mashable for iPhone
My Octocat by Github