I've never found anything of actual use on StackOverflow in my ~decade of doing this professionally. The only time StackOverflow provided useful answers to my questions was during my first year of programming courses in university.
There's some useful information there. It sometimes takes a lot of digging, especially if you're dealing in things that have existed for a long time, but change a lot (UI stuff tends to be pretty bad, questions from 5 years ago rank highly but are nearly useless because it's three frameworks ago).
Also, I was able to cargo cult an applescript accessible objective C program utility (returned the color of a specified pixel from the screenbuffer) from stackoverflow without having to actually learn anything about objective C. That was mostly because the online sources to get started on objective C weren't geared towards writing a short one off program; Apple's documentation in general is hard for me to process.
Thats why I put in the "know how to ask questions" part. Sure, a lot of the time you don't get an answer. And you end up figuring out stuff the hard way yourself. But then I always force myself to go back and answer my own question. It might help the next guy, but more importantly if I have to answer the question myself I need to put what I learned in writing.. and in an understandable way as well. Often the exercise of explaining it will make me understand even better.
It's pretty nice for "is this thing I've encountered in this (API/library/SDK/tool) with no public issue or bugtracker a bug, or am I screwing up?" sorts of questions.
