As announced last sunday on the official developer blog, Facebook started to remove application-tabs functionality for user-profiles this wednesday. Tabs provided by applications already installed, can’t be added to a user-profile with the “+”-link anymore, and both FBML- (fb:add-profile-tab) and FBJS (Facebook.showProfileTabDialog)-methods for using the “Add Profile Tab” dialog display an error message (see screenshot). Unfortunately, the official documentation doesn’t reflect this change right now [1, 2].
Tabs which have been added to user-profiles before wednesday are still displayed, but contain a warning message that they will be removed soon (starting November 3rd, more precisely).
Note: luckily, this change doesn’t affect Tabs on (Fan)Pages, as explicitly stated in all official announcements!
On the positive side, this change continues to simplify the Facebook Application-Developer-settings, as the option weither an application-tab should be installable to user- and/or page-profiles is now gone at all. On another note, this should also fix the long-missing Amin.setAppProperties-attribute for programmatically making apps available to Page-tabs (see more details on the bug-tracker).