I have exactly the same problem. We have a Seam 2.2 application without EJBs. The application ran very well on JBoss 4.2.3. After mirgrating to JBoss 5.1, the memory consumption increases from 220MB to 680MB. In addittion, we encounter similar performance issues.
Btw: The startup time of the 5.1 server is four times slower than the 4.2.3 server having similar services running.
I would be really glad if someone could clarify!
You'd think there would be rigorous QA @ JBoss for JBoss 5.x releases in conjunction with Seam 2.x apps. It's always safer to wait at least 6-12 months for JBoss products to stabilize.
Have you tried baselining the hotel booking app with 4.x and then comparing performance with 5.x???
Well, the obvious thing to do is to use a profiler and find out where it's slow...