Good luck with that.
It seems pretty transparent to me: you can verify the Bitcoins were sent, you can see the amount they were cashed out for (and compare to historical price), and they post confirmation numbers so if you were so inclined you could probably call up the Human Society and tell them that you had a few people get together a donation and you'd just like to confirm the amount for it and give 'em the confirmation number.
I see it as a means to an end: instead of standing around with the typical libertarian circle-jerk of "private charity will take care of all" with no one actually doing anything... if, in a few years time Bitcoin's going strong and for example Medecines sans Frontiers has received quite a bit via this site and others, it may prompt them to accept them directly. In the meantime, some actual donations get made, rather than pure talk.