Shoutbox

I've been thinking similar for a while actually.

Subforums are only visible inside other forums.
I think you're talking like forums inside as section like "Forum & Website" is inside a General section. However "Poll Centre" is a subforum of General Chit Chat.
The main difference is subforums aren't visible on the front page, which makes them less useful to "noobs", who won't bother looking into these places.

In Messenger & Technology I'd like to see a;
MSN/Windows Messenger Support forum

However, I wouldn't like to see it lead to forums being made for individual plugins, which just gets to be a pain (I'm thinking StuffPlug mainly).