A feature that is really helpful in other forms around the net: "find all posts/threads by (username)"
This is good for keeping track of your own posts, if you posted in a few threads but aren't watching them closely.
It's also useful collecting information from a specific person. For example--someone working on a similar plan or with experience making a particular thing work, especially when it crosses several forums.
This could also cut down on excessive PMs from newbies like me