Actually, that's the one thing they're not good at.
Ironically enough. Set-trees can easily give you ALL ancestors, but not just the immediate parent. However, forum software is (usually) only concerned with the entire tree.
So, I added a parent ID field that gets prefilled at post creation time. It's never used for navigation or tree display though, just that link. :-P
Regards,
-scott anderson
"Welcome to Rivendell, Mr. Anderson..."