I love the idea of the donating via BTC.  Assuming you are worried about the write-off, I see two issues. BTC is more anonymous than the government would prefer.  Demonstrating you donated BTC has some inherent difficulties (at least with the US IRS).  The other item, I'm not sure how many flags I want to flag for the IRS.  Being audited is no fun.  Trying to explain BTC to the auditor would be quite a chore.