Usefull for debugging html/jsp
JDO 2.0 has been approved as the standard for object persistence within the JCP.
I have used the JPOX implementation which is an open source solution. I must say the feedback and support on that site is quite good.
If I had to choose between JDO and Hibernate I would choose JDO since Hibernate is strictly an O/R implementation at this point, and does not follow a specification like JDO does.