The one thing I find missing in other persistent object implementations is the ability to persist data from any kind of source. You could easily persist data from a Web Service, a dataset, other functionality found in your business logic. Just about anything...
Another aspect of creating persistent objects is the ability to design these through a visual designer such as the DataSet editor in Visual Studio. One way to go about using the same designer and get an output consisting of your objects instead of a strongly...
One of the things that are cool with .net Framework 2.0 is the ObjectSpaces. For JAVA developers this has been available for quite some time through libraries such as Hibernate. Today you get Hibernate for .net and there is also a free Objectspaces library...