There have been a number of posts here from people using Glassfish, I'd suggest using the forum search for Glassfish.
AFAIK, people have Seam apps running under glassfish, but it takes a little more work on the config files.
There is also a glassfish example in the seam distribution
The "examples/glassfish" shows how to use Seam with GlassFish EJB3. The "examples/jpa" shows how to use Seam POJO and JPA in Glassfish (as well as in WebLogic 9 and WebSphere 6)
Thanks guys for the good info. My problem that I am hitting is that the 9.x series of Sun's application server is based on Glassfish, but the 8.x and later are not.
I have been working on setting up a "hand crafted" set up from the glassfish examples and just about had it. The only problem now is that org.jboss.seam.Seam imports javax.persistence.Entity and from what I can tell, it is brand new in JavaEE (as in EJB 3.0). I'm diving through examples but haven't been able to get around that little tid bit. Any thoughts?