We're having great results with the Phusion stack (Passenger and Ruby Enterprise Edition) in house, but I haven't been able to find much in the way of data on their use in the wild, particularly REE. I'd love something akin to WWR's High Profile Organizations Using Rails or Ben Forta's Who's Using ColdFusion? list.
There's some google group activity on this, but I'm looking for something more, for lack of a better word, PHB-friendly.
Passenger is being used by a lot of people including Engine Yard.
REE does not have as widespread adoption.
But the same was true of jRuby before too, now many are using it.