Flávio Coelho has been looking at various ORMs and other persistence
mechanisms for Python; a while back in response to one of his blog
posts I pointed him at Durus; he has recently done an exploration of
ZODB:

http://pyinsci.blogspot.com/2007/09/zodb-vs-relational-database-simple.html

And now ZODB and Durus:

http://pyinsci.blogspot.com/2007/09/zodb-vs-durus.html