I thought I'd suggest implementing a message preview button to allow for seeing how the message is formatted and looks before actually posting it. This, along with line numbers, would allow one to more easily refer to line numbers in code (s)he is posting, instead of going into edit after the fact to make changes.
I agree, that would be a good idea, it might also help by making some people re-read their posts and notice the errors in tags that they are using, like [code]/code]