The problem with a thank you message is that you still need to open the thread
to find out if it has been solved.
Partially this would be useful for people doing searches, as they could focus on the ones marked solved first, but secondly (and more the reason I suggest it) is that when I pop on to Perlmonks and check through the newest nodes many have already been satisfactorily answered. On the other hand, others may be complex or just get lost in the shuffle. Anyone who frequents the PM must admit though that unless your thread gets an answer in the first day or two, or you have a thread going with someone, a question is likely to stagnate. Maybe instead of a solved flag allow users to push their questions onto a still seeking Perl wisdom list...
Basically from my end I would like to be able to easily catch a few threads that haven't received help, which are often one of two types, the ones that need some specific expertise, or the inane ones. The ones that need specific expertise benefit most by having many eyes hit them, so some mechanism to keep them visible would help.