It seems like the SideShow team is really getting things together now. This week Windows SideShow for Windows Mobile is shipping as a developer preview. this lets you use your Windows Mobile device as a Windows Vista SideShow display.
I have shown this in various demo situations over the last couple of years and now you can get your hands on the technology and start building for it using the new Managed APIs.
Also be sure to check out the SideShow gadget development contest NVidia is running.