I've finished reading an interesting article about Windows Vista, interesting because is oriented for technical people (IT, developers and advanced users).
It's the first article of three that will be published, but gives a good overview of some of the changes this operating system brings.
I like ars Technica because they don't usually get into "politics" favoring Windows, Linux or Mac, and here it's reflected too. For example, talks about the DRM system (Media Foundation), explaining what it does, and who benefits (companies), but not going into stupid and false affirmations that it cannot play "any copyrighted material".
Anyway, the article speaks about Desktop Window Manager, the new Driver model, DirectX, Media Foundation, and the .NET Framework 3.0 basics (mostly talking about WPF and it's vector-based graphics).
Very recommended reading.
Oh, and by accident I found this article of Vista's UAC for Game Developers, very important too if you plan to make games with XNA compatible with the XBox 360 (because as UAC states, games should only access to a few special folders, for example to save the game data).