The Bookmarks add-on has been implemented.
It is currently available to Premium Contributors only.
I appreciate that is a bit of a contentious issue, but there has to be some way of rewarding those who financially support the site and pay the hosting fees every year.
It's fairly straightforward to use, just click the Bookmark link bottom right of a post of profile post.
An overlay will appear and you can decide to add a note, set it as a public bookmark and sticky it.
Any public bookmarks, thread or profile, will appear on a member's profile under the Bookmarks tab.
To manage your own bookmarks, click on Your Bookmarks in the account menu dropdown:
Or directly on your profile page:
From there you can view, edit and delete your bookmarks, toggle the status between Public and Private, and click on the note and post links to read the contents. Thread and profile bookmarks are conveniently separated on two different tabs, making it easier to manage them.
You can also set alerts for various actions related to bookmarked posts.
Hopefully you will find this a useful feature.