I realize that it is completely my fault when I post to an old thread with my two cents of information that doesn't matter any more. However, on more than one occasion, I see a thread that has been bumped up because somebody else posted to it, then I end up posting to it, then other people do, then a moderator closes the topic. Couldn't this all be avoided with huge red bold lettering "This thread has been idle for __ and probably shouldn't be posted to." when the message has been idle for over a 2 weeks or "This thread is _ month(s) old and should be closed. Please start a new thread." if it is older than 1 month from the original post.
But hell. I've seen moderators do this for old topics that had very few messages and the latest message actually answered the poster's question in a useful way.
Anyway... just a thought. I know I would be less inclined to and post to an old thread if my whole screen showed this message