I'm a big fan of the update paragraph.

The ++/-- votes already serve the purpose of rating and a solved checkbox isn't going to really add anything to the thread that an edit-and-updated paragraph wouldn't.

Perhaps there should be a js button that you can click to add:

updated 8/15/7: Thanks you guys! jettero's answer was correct.

But even that is silly since we can all type to have been able to post here in the first place.