Perhaps you weren't aware that EFF is a "digital rights advocacy and legal organization"? If we can imagine that Bitcoin might have legal issues, how could that have escaped the people at EFF?
I'm aware of that. I'm just saying it doesn't follow that they put it through the rigorous examination you seem to imagine, given that e.g. they may not expect many such donations, had more pressing priorities, knew it would have issues but were prepared to be the test case, etc. Or maybe they just reasoned, as you are doing, that "X accepts it, so it must not have legal issues", not expecting the pseudo-evidence to cascade to others.
What I wrote originally was that EFF's lawyers must have decided that Bitcoin is not clearly illegal. You seem to have interpreted me as saying that they decided that it is clearly legal.
Now you can donate to Singularity Institute using Bitcoin.
Currently Bitcoin mining appears to be profitable as only bubble economics can be. Already some Less Wrong users have purchased GPUs and started mining Bitcoin. Please consider sending some Bitcoins to SI at address 1HUrNJfVFwQkbuMXwiPxSQcpyr3ktn1wc9
2014 Edit: Please donate Bitcoin by using the Bitpay link on MIRI's donate page. Thanks!