My company is evaluating Seam 2.0 and I have a concern. There was a forum post back in September which suggested that OpenJPA does not work in Seam 2.0. As per Gavin's request the poster submitted a bug (JBSEAM-1946). My concern is that the bug remains unassigned with no comments. I have not personally tried to use OpenJPA with Seam 2.0 but perhaps someone here can provide a quick answer that will save me some time.
The obvious answer would be to use Hibernate instead of OpenJPA, however we find OpenJPA's annotation-based implementation of JDO fetch groups (which Hibernate docs refer to as "mostly a marketing feature...") quite useful and are making good use of them in several applications.
Gavin did make some fixes pre 2.0.0.GA in this area, so give it a go. Let us know how you get on, and what problems you get. The fixes *should* be straightforward.