One of the frustrating aspects of assisting the community by providing answers and solving problems is when the OP acknowledges that one or more responses has answered the initial question and/or resolved issues that are subsequently mentioned in the thread but fails to accept an answer.
In these instances it was possible in the MSDN forums to propose an answer even if the OP never returned to the thread to mark it. At least there would be some indication that there was an available solution and by reading the thread a user could see that the OP had actually accepted the proposed answer.
So I have two suggestions for consideration -
Implement some form of disclosure for proposed answers.
Allow moderators to accept answers in cases where the OP has acknowledged the provided solutions but has abandoned the thread.