If you ask me, I think there’s lots of room for GlassFish for new development and applications. If you ask my customers, they’re keen on being able to migrate existing applications to GlassFish.
For those people, the AVK and the GlassFish Migration tool are great assets. What make the tools even better is sample code and experience fixing what took can (yet) migration automatically. Sekhar has one such example where he goes through the variations on library (facelets), JNDI naming, persistence provider configuration, and packaging of an existing application on its way to GlassFish. Most of the changes seem to be resulting from the AVK triggering warnings or errors. Note the AVK is available also straight from NetBeans.
Wether you’re looking to migrate to GlassFish or simply interested in what it takes to write portable applications, Sekhar’s blog is a great one to follow.