I saw a similar suggestion here to bookmark threads or posts to keep track of them, but I feel that a useful feature would be to allow members to mark an entire forum as a favorite. Then, from a button or link from the home page, being able to toggle displaying only your favorites, or all...
I would really like to see an addon released that gives usergroup controlled profile enhancements. This would increase account upgrades.
Here are some features that could really upgrade profiles:
Profile Widgets / Blocks
Audio Player with playlist...