Definitely works in Asia, usually works in Europe and UA hubs, sometimes works in all other cities. A random collection of red tagged and no tag bags rolled off the belt this past Sunday at JFK.

On a side note, I realised after a weekend trip to SFO that our bags were not tagged priority, which seemed rather strange given all the talk at SFO check-in about the line being only for UGS/1K...then I realised that the bag was tagged as Mrs. J-H (no status, no P on the tag itself) - so you want to make sure that the baggage tag has the status holder's name on it (my wife and I were on the same locator, she just passed her ID first to the agent), otherwise you will risk it not being tagged properly.