I have been doing a very small lab with an object-oriented database, db4o, and I am very impressed indeed.
The concept a first is a bit hard to grasp since there are no tables, no SQL and hence no mapping going on. You simply store your objects.
Of course the trick is to query them back, but the excellent db4o-crew and chunking out code every now and then and for example the current release includes full support for LINQ which gives you and excellent programming experience.
I am still very much a newbie and have some un-answered questions on how data and class definitions evolution is handled. But it looks cool, very cool.
Just say it loud for yourself: “No more SQL. No more mapping.” Yeah, you like it, admit it.