I have been using SO for a while now, and only recently registered myself. But something that bothers me is people who ask questions and then don't accept an answer. Now, I know this is a very robust problem, but I propose something which might help the whole situation.
Many people create user accounts here, or ask questions without full accounts and then either just copy-paste the answer and leave, or say "thank you" and leave. Without ever accepting an answer.
What I propose is for any "new" accounts to have a "beginner mode" something like this idea: (highlighted)
When a "new" user comes to an answer to his question, he will be asked "did this answer your question?" either under/above/instead of comments. And he will be shown two buttons "yes" and "no"
This way it's much more intuitive for new users to the site who want to simply ask a question, but don't understand the convention of accepting answers.
Pressing "no" could bring them to the comment box, so they can clarify or whatever, while pressing "yes" will mark the answer as accepted.
Of course, this "beginner mode" could do other things, but I am specifically frustrated with the lack of accepted answers by new users.