The first is application tabs on user profiles. Originally introduced around the period of time in which Facebook was initially booting profile boxes off the profile page, Facebook says today that it will be removing app tabs in Q4 2010 due to “low usage rates.” After the removal of app tabs from the profile, and the upcoming removal of the boxes tab, only tabs devoted to Facebook’s in-house applications like Photos, Videos, Places, and Notes will remain.
In addition, Facebook has posted that many of its old REST API methods would no longer be supported after the end of the year (full list here). Instead, developers should be using Facebook’s newer Graph APIs.
Finally, Facebook says it would be deprecating the <fb:editor>, <fb:board>, <fb:wall> and <fb:feed> FBML tags, as well as the Data Store API, by the end of the year.