- Persistence Manager can do a lot of great caching, so you don't even have to go to the database (which is the #1 bottleneck)

- Tools allow us to push the data mapping OUT of code. I can view my database and point and click my way around.

- Relationships are a *lot* easier to manage in my opinion. I think it is a lot nicer to be able to say:

Cat poorCat = getPerson().getDogs().getLastCatEaten();

to traverse the relationships. Nicer than working with joins.

However skill-set does come into play. If you are an SQL geek, then you may want to stay in that land. JDO is not a silver bullet by any stretch, but it is an interesting technology, that will mature and become a great way to access persistent information (not only RDBMS)