I see topics posted in the wrong forum fairly often, and I usually comment and say what forum would be appropriate. Sometimes the topic gets moved by staff, and occasionally even re-posted by the OP, but usually they just stay where they are. I'm taking the time to comment anyway, so the ability to notify staff of the problem would be very helpful to both me and the OP. I know this is a minor gripe, but often it's just a matter of trying to make sure the submitter gets the help they are looking for.
(p.s. I know there is an "other" category on the report form, but I would feel bad using that for something as small as a misplaced post.)