The latest SexyBookmarks version 220.127.116.11 places an annoying ad banner at the top of every WordPress admin page, with no user option to remove. I finally found a solution here to comment line 1791 of wp-content/plugins/sexybookmarks/sexy-bookmarks.php.
However, commenting only line No 1791 just gives you an "X" to close, and then only for 30 days! To get rid of it entirely I had to comment out both lines 1790 and 1791:
What an irritating P.I.T.A, that I have to edit code to get rid of this crap! Makes me start thinking about switching to a different social plugin!