Minor nitpick: I find it rather silly when people say "a full x percent" (as in, a full 89%) of something - either you're being correct and specific, and you mean 89% exactly, or you're being fairly specific and mean 89.124535% or something. You wouldn't use it to mean "around 89%" or "just under but close to 89%" - you'd round down to 88% or, again, be specific.

This was an excellent article, though - something I have thought about fleetingly before but never really considered. My personal area of interest is animal rights, which is a lot harder to evaluate (also, I'm not in America, so GIveWell probably hasn't evaluated any charities which I would donate to) - however, it's given me a lot to think about, and a new way to approach charity.