I once found an answer to my question from SO, tried to upvote it but SO didn't let me because it was my own answer to the problem written over a year ago.
It seems StackOverflow works well for seniles as well.
Depends - I've seen stackexchange questions that are exactly what I'm looking for and I would argue are on topic - only to see that it has over N thousand views with a note saying "closed due to offtopic" by a moderator.
Don't even get me started with those people who go through the site editing posts to change the link that someone posted because they don't agree with that site.
Don't get me wrong - there are some great answers on stackexchange sites. But too many times I've seen someone ask a question, a response with "no that's not possible" then another with "actually that is possible".