I'd like to be able to "subscribe" to forums, such that I could then look at a page like "What's New?", but filtered to only show updated topics from the forums to which I'm subscribed. For example, let's say you really want to stay on top of the "Announcements", "Bug Reports", and "XenForo Development Discussion" forums here. You'd just click a "subscribe" link, then view the respective "subscribed forums" link for a quick view of what's happening in the areas of the site you're interested in. vBulletin's "New Posts" search has similar (but somewhat hidden) filtering functionality, though it wasn't fully baked in to the software: you have to append "&include=XX" parameters (where 'XX' is the forum ID number) to the URL craft your own search results ("&exclude" was also supported), but it is still a very useful feature that I have taught many of my users how to use. A more comprehensive system built into XenForo would be very useful and should be fairly straightforward to implement.