Hello,
A new option is added today: favourites.
You can bookmark users, topics and individual posts. Each post has a link, you've probably already found that one, to add a whole thread you need to use the threadtools menu in your navigation bar and to add a user to your favourites you need to go to his/her profile.
You can see all your favourites in the usercp, that's where you can manage and delete them too.
Bookmarks