When you click on the My Bookmarks tab, I think it would be extremely useful to add a small little Comment Box out to the side to make little notes in. I have many bookmarks that are fairly old threads that went many many pages, but can't remember why I bookmarked them. One thread is full of gifs that I bookmarked because there was one in there that I wanted to keep for later, but it would take quite a while to find the exact page number it is on.
With a comment feature, a poster could make a little note denoting what page number or the reason they bookmarked a thread, and would be a valuable asset in the bookmark department.
Just something to think about