Earlier quoted context omitted.
Agreed about the importance of making sure you donate to the right charities, which is why I was disappointed to read this: "And, to begin, they have sprinkled $1 million on Silicon Valley nonprofits that focus on everything from urban forestry to homeless families." Another good essay about this stuff is here: http://lesswrong.com/lw/3gj/efficient_charity_do_unto_others...
For what it's worth, those six nonprofits weren't just chosen randomly. Each GP picked one he and his family had direct experience with. For my part, I don't know as much about this as some people, but my wife teaches philanthropy at Stanford and has studied, written about, and taught the topic of effective giving for her whole career, so that works out nicely for me. (Can't resist plugging her recent book "Giving 2.…
For example, if a16z said "Hey users of instagram (or users of a16z product that just sold), we're going to let you decide which cause some of this money goes to," would that create a delta in value from the original proposition?