Wotif.com, my employer, went live on Glassfish in mid January. I was the driving force behind the move. You can read about it on the Glassfish site here: http://blogs.sun.com/theaquarium/entry/how_to_run_a_top .
There is a questionnaire linked from the entry that is the raw question and answer source for the entry. You can see it here: http://blogs.sun.com/stories/resource/wotif/wotif_responses.html
Though not one of the main reasons for the change, we find ourselves on the JEE5 platform, and liking it. XDoclet boiler plate generation and EJB in-container testing are things of the past. It took a few days to move our code from EJB2 to EJB3. The end result is that we find ourselves early adopters of JEE5. The opportunitites this presents and some neat ways of capitalising on them are being documented on Robert Watkin’s blog. See http://twasink.net/blog/ .