I run a blog with several users/contributors (http://qpdx.com ) that are not always html savvy and often their toolbars are missing key buttons.
I am an admin and the only button that has disappeared for me is my "more" button toolbar. This has been going on quite awhile but I always just switch to HTML view (which does actually have a button, although you don't really need it) to enter the code.
But I recently set up an a new user as an Editor and her "Link" button was missing in addition to her "more" button. When I upgraded her to an admin the link returned but the more did not.
Then I made another admin account and she doesn't have access to the kitchen sink menu from her visual view at all and I cannot bring it up with keyboard shortcuts. She is able to switch into HTML mode and access the "Link" button from there but it's quite tedious and annoying. So I'm finally realizing I should take care of the issue as a whole. Any help is welcome.