The seam community site went live exactly one month ago, and already boasts more than 1000 registered members, with twenty-something people signing up every day. The new forum is buzzing, and we're starting to get lots of useful information up on the wiki.
One of my first tasks since starting at JBoss/Red Hat was to investigate and document container interoperability. What I found is what I expected - various tweaks, settings and library requirements depending on what container is being deployed to. These have more to do with specific server needs rather than anything Seam is requiring (mostly).
The last year we have been working full time on JBoss Tools and JBoss Developer Studio. One of the challenges we had were to add support for JBoss Seam in Eclipse. Similar to what the Seam team did for the underlying frameworks (JSF, EJB3, JPA, etc.) we had to do integrate/adjust for the various plugins that exists in the Eclipse family (WTP, JSF, Dali, etc.).