Wow. Dave put a hell of a lot of work into this post on database object-relational persistence frameworks. It's a great job, thanks Dave! (But Dave, we ALSO want to hear about your personal life. No censoring!)
My job today, literally, is to study TopLink to really grok how it works so we can evaluate its continued use here. I'll pass along my additions to the framework graph for Toplink to Dave when I get a chance.
Also, I just noticed this on Cafe au Lait:
XORM beta 2 is an open source, "extensible object-relational mapping layer for Java applications. It provides interface-based persistence to RDBMSs using the Java Data Objects (JDO) API while allowing developers to focus on the object model, not the physical layer." XOTRM is published under the GPL.