I have been working on the open source Jaffa web application framework (as a paid consultant) and we use JBoss as a platform. Sure there is a learning curve for building on JBoss, but it is a stable and flexible platform.

I think that IBM's Gluecode web app stack seems to fill a different need: Gluecode is very polished and a turnkey solution for development and deployment: a better solution (I think) for some web applications because of the the simple administration functionality. I would feel better about delivering a web application to semi-technical customers that was deployed on Gluecode.

BTW, you might want to give Jaffa a try: there is a steep learning curve but it includes builtin business patterns, automatically generated CRUD backed web forms (generated from domain models expressed in an XML notation), etc. Cool stuff - check it out.