I certainly understand the sentiment and would love to do the same.  I expect I'd have no problem with pretty much all organisations that would be considered for support.  I would however refuse to donate to organisations such as Monsanto or the RIAA and for this reason alone simply cannot say "I pledge 1 BTC to any charity/organisation which adds a Bitcoin donation option".

Generally, I won't be upset if Bitcoin100 money ends up going to causes I wouldn't usually donate to.  As you noted, such pledged money is much more like a donation to Bitcoin itself.  If a cause comes along that I really do want to donate to (TOR, Free software foundation, archive.org) then I will make a serious donation on top.

I would be dismayed if the Bitcoin100 didn't manage to get 100 new charities to accept Bitcoin.  It would be a great shame for us to only get through 5 or 6 charities before fizzling out due to there being too much caution.  Just my thought though.