Each user would be able to configure this themselves.
They would be able to create a "New Posts" category, call it whatever they'd like. They should be able to create as many as they want.
They then select which forums (and maybe blogs, etc) they would like to include in this category.
Then they go to a custom page that displays all of this information on it. This way, they are only looking at forums they want to see, can simply click the category header and a new post search is done for only those forums.
This actually prevents posts from getting lost in the "What's New" page on the secondary pages, etc. Many people only ever read the first page. But on forums like mine, we have about 100 forums and the what's new page is fairly useless to see content you're interested in (not everyone is interested in all 100 forums. heh).
Admins should be able to flag each forum as to whether or not it can be excluded. Essentially forcing specific forums to show up.
This is somewhat like the Selective Forum Filter hack (that I currently use), but this is much more configurable and useful in my opinion.
Anyway, just another idea. My own forums are getting so large that I can't keep track of just the forums I personally need to and this would be useful.