If someone attempts to post the same subject in multiple forums, usually one of the following is true:

1) Neither post is in the right forum.
2) It's spam.

I see a lot of 1) when people post to the 770 and 800 -specific forums, in which case, simply saying "blah on the 770" and "blah on the 800" is enough to differentiate. Not that they should be cross-posting anyways!

I'd like to see BOTH posts deleted, but I'd settle for preventing the second post from being created.

I see far, far too much of 2), but this simple step would solve problems like the one I'm seeing right now: four "active topics" that are the exact same spam post by the same user.

Have you used the post warning feature?