It amused me that when Heroku released their Java support a while ago, they trumpeted about how it was going to free us from the tyranny of 'containers'.
They then proceeded to show an example of how to fire up Jetty (a servlet container) on heroku.
Ho hum.
I've recently done some Grails dev on heroku, its very nice. The deployment model (push source to them, with it being built remotely in Heroku land) takes a bit of getting used to and needs commercial approval to use, but works well for what we needed.