I am about 4 months into a project using a very expensive object persistence mechanism (Franz Lisp AllegroCache) that almost automatically wraps Common Lisp CLOS classes for automatic persistence and B-Tree indexing of as many slots as you want to tag as indexed. As is sometimes is the case, here commercial software tools save time and effort. There is a very interesting open source project for Common Lisp (Elephant) that does something similar by using BerkleyDB or a relational database as the backend – it looks good, but it is not yet an out of the box solution.
For Java work, although I was once a fan of Hibernate, I try to use Prevayler instead: if you add new instance variables to the end of class definitions you can add to your object model without breaking your persistent storage – a neat trick, to be sure.
When it comes to the best programmer productivity using object relational mappers, I personally think that Ruby Rail’s ActiveRecord wins hands down – with the slight cost that you design database schema instead of class models.