Back in, I think, 2002 I went to JavaOne and the most over-subscribed sessions were on JDO, literally queues out of the room. Since then it sort of died a death and with the Hibernate/EJB 3.0 approach taking over the OO persistence layer surely the battle was lost.
Just kicking off a Google App Engine 4 Java (thank you Google, I can code like a human being again) session I note with some amusement that they've picked JDO as the persistence layer. It makes sense for what they do and the sort of store they provide but I still find it quite funny that I'm now dusting off those JDO pieces that back in 2002 I was sure would be the future but about which I was proven wrong.
Until today ;)