Directly under the subject field would be a drop down.
Whatever the user selects from the drop down will be inserted into the body.
The value's for the drop down need to be independent for each board.
Whether the drop down is required to be selected or even visible should be independent for each board.
What's it good for?
Lets use Infopop as an example. They have a bug board. They request 'Please include the Version number in your subject.' Instead of hoping someone includes a version number, all the versions could be placed in the drop down and the user would be required to select one.
Would be create for tech support. Could be used for other boards, such as a Ford Mustang board where the drop down includes engine sizes.
Basically use it any time you have a board where you need to force the user to include some specific info in the post.
I need something like this too, but I want it in the subject.
My users posts quite a lot of short stories, and the ability to have a menu that lets the user ad a few pre-defined labels would help not only when browsing for stories with a specific theme, it is also something that should be added to the search function!
Different labels for different forums would be cool, but not at all necessary.
If you´d want it to be in the searches it would probably be best to have it as added fields to the post rather than as text added to the body post itself.