I don't recall ever, before I null routed all the Facebook domains on my machine, having come across something useful and programming related on Facebook. StackOverflow and Hacker News (and to a lesser extent proggit) are places I go.
I often find myself in StackOverflow when searching for a solution for something in a language I'm not very familiar with. Sometimes you end up being forced to do a little maintenance in a language you don't know well and StackOverflow often has answers to common-ish questions.
I was more contributing to Stack Overflow than asking. Frankly I used Stack Overflow just once to ask a question for a problem I though had no solution. And surprisingly I got the solution within a day. The best resource for programmers ever!