I have only seen it once, off the BAH flight arriving into LHR on 6/April 2012.

No idea who it was for though! But I was in CW and the F cabin seemed to be empty as I was getting off, which raises the possibility that the passengers were either in CW, WT+ or even WT!

A really nice benefit of this service would be being able to linger a bit on the plane and get all your stuff ready to disembark after landing rather than having to go through all the hustle and bustle.