I oppose adding [RESOLVED] to the subject, this means changing the subject to a complete different string and detaching it from the thread. not sure how this would work for google groups, but many people (me included) read on gmail, it happened to me not long ago (can't remember which mailing list it was), someone added a {RESOLVED] at the end of the subject, meaning I got an email detached from the discussion.
if someone would post a message after they got a solution they could just add RESOLVED to the first line of the body and then post their conclusions on how they got there. problem is that often people go silence when they achieved the solution.
also take in consideration that some posts are discussions like this one, not answers to a specific problem.
avraham