Those who spend time helping to provide solutions deserve, but very often don't get some positive feedback. Maybe showing something as solved isn't treated by everyone as being significant but you have to take what you can get. As mentioned, many op's make a single post with their issue and are never heard from again. I think it is worth encouraging people to provide answers, otherwise this whole process doesn't work. If that encouragement has to sometimes come from the forum (through the moderators) instead of the OP, then that's ok (with the understanding that it's a bit more work for the moderators). To make it easier for the moderators, it would be good for other experienced contributors to recommend posts that deserve to be closed as "deemed as solved". Maybe there should be a separate status for ones that are forced to solved status rather than shown as solved by the op (even though they would both count in the solved count). For anyone who is looking for a solution to their current issue, finding an old post that is "deemed as solved" provides a higher level of assurance that it is a correct answer than nothing as all (i.e. dead silence).
On the flip side, I think that anyone who makes a post that is replied to but then does not provide any feedback (pro or con) within a certain period of time should automatically lose reputation points (with the rules updated appropriately). It would also be …