3.1 RC1 problems for me.
Facebook log-in not working.
Added the App settings as described.
I log on using the small Facebook pop-up window, approved the app and nothing happens.
Avatar not showing up in the ad management in the back end.
Pre 3.1 too
Existing ads are not updated after a new Custom Field in front and back end. (I would have to delete an ad and then recreate it to see new custom field)
Advance search is affected of course if you have no data to search for.