The FBML application is going to be going away as of March 11th 2011 If you already have the app installed, and are using it, it will continue to work just as it does now
However, after 3.11, new page owners who do not already have the FBML app added to their pages will not be able to add it. So if you or know people starting new pages, tell them to install FBML immediately. http://ping.fm/Nd9xo