[Phillip Burger]

It would be quite useful if while you were looking at a topic, there was a timed AJAX request (or similar feature) checking for updates to the Topic and letting you know when it is updated.

Think about how if you are in Gmail and an update comes to an email thread – it lets you know, so you can read the update before you reply.

I find in quite a few forums that you are reading and maybe forming a reply, just to update and see that someone else replied while you were on it.