The next beta build of Windows Vista will include the Sidebar.  That's good.

The build will only include 5 gadgets.  That's bad.

You will be able to get more gadgets from MicrosoftGadgets.com (and DesktopGadgets.com eventually).  That's good.

Most of the third party gadgets are awful. That's bad.

There's a guide to make your own Microsoft gadgets. That's good.

The Microsoft gadgets are made using DHTML. That's bad.

Stardock plans to find a way so that gadgets can be made in a non-crappy manner such as XAML/WPF.

But in the meantime, check this how-to guide.