My college professor used to (still does I bet) proudly put the stack overflow 25karma point sticker and a letter of thanks from the admins on the door to his office. And this was a man with tenure etcetera.
It's entirely possible that the support he received from others outweighed the time he put in supporting others. I know for sure that's the case for me.
In my experience, SO is only useful for trivial questions, or maybe questions that ask for a better explanation of some basic concept. If you have a question you can't find answer for by searching on the internet, it won't be answered on SO either. I still occasionally help people there, but it was never a useful resource to me personally.
For the most part I agree.. I do wish more people would simply do a search before asking some questions though... I see way too many lowball questions, and it's impossible to keep up with the hose/feed even on relatively narrow topics anymore.
SO is most useful for questions that could be answered with a simple google search if only you knew the right search terms to use. For more complex questions, it's only occasionally useful.
You could almost see them starting to think 'Oh shit. Someone is getting screwed here, and I'm pretty sure it's not Google.'