I have been seeing a lot of questions on here with answers, but most don't seem to have accepted answers (the check mark thing next to the answer comment). Based on my (limited) experience with SO, this is important for closing a question as being answered. Should we be flagging the answered questions to be accepted? Thanks! :)
Actually, it isn't very important at all. All it takes for a question to be marked as "answered" is either an accepted answer or one answer with a positive score. So just upvoting an answer is enough to mark the question as answered.
Also, accepting simply means that this was the OP's personal favorite answer. It doesn't indicate the best answer, or the simplest or the most beautiful. It's just the OP's choice.
That said, on the sites I'm active on, I tend to leave a comment like this when I see the OP leaving thank you comments:
If this answer solved your issue, please take a moment and accept it by clicking on the check mark to the left. That will mark the question as answered and is the way thanks are expressed on the Stack Exchange sites.
I try to only leave such comments when the OP has commented on an answer. The objective isn't to badger the OP into accepting an answer, it is simply to point out that instead of leaving thank you comments which are just noise and clutter up the site, they should accept the answer and that's how thanks are expressed here.
So, I would say that if the OP has not given any indication that they've read an answer, asking them to accept is pointless and pushy. If, however, they seem to have appreciated an answer and yet haven't accepted, then maybe they don't know how the system works and we should leave a comment like the above to inform them.
Please don't prod users into accepting answers. The system already prompts users to accept an answer at an appropriate time, but accepting an answer is a completely voluntary activity, and it is up to the user to decide when (and if) they choose to accept an answer at all.
Such comments might seem like a harmless reminder of a feature a user may simply have forgotten, but the folks looking on will imitate what they see… so as the sites start to fill with "please accept an answer" , "can you accept my answer?" … it starts to become somewhat noisy and annoying (and even a bit harassing) to just about everyone else looking on.