Is there really an opportunity cost? There are tons of companies, non-profits, and academic research being conducted in the medical and other more worthy spaces. It's not like the existence of Facebook changes that. Also, the tech talent wars are really only driving up the costs of Computer engineers who are interested in the social web. It's not like this impacts non-profits very much, they are still getting talented people, they just don't happen to be in the market for CS engineers.