I would be very surprised if .NET includes any sort of data model. .NET, like J2EE, provides you with plumbing to create your own applications. But you have to start from scratch.
Back when Enhydra was a viable contender in the open-source J2EE space, I asked one of the project heads why they don't provide any applications or data model. He said that this was a conscious decision not to interfere with the vendors of add-on applications.
I suspect that Microsoft has a similar viewpoint. Namely, if they provide a data model as part of .NET, then (a) it won't be appropriate for everyone, and (b) it'll mean that Microsoft is competing with their own integrators and vendors.
So while .NET has all sorts of fancy database-access methods and marshalling systems, I expect that you're stuck doing all of the database work on your own. This is where OpenACS has a big win, for sure.
