Soon you won't be able to swing a dead cat without hitting a copy of the February CTP (Community Tech Preview) of Windows Vista (you can get it on MSDN subscriber downloads now). I've installed it on a couple of machines already, and so far the experience has been pretty good.
One of the cool things you can now do with the February CTP is develop your own gadgets for the new Windows Sidebar. It's pretty simple to do, and requires only a little bit of HTML and XML and a text editor to get started. You can learn more about creating Sidebar gadgets here:
There's also information on building gadgets for Live.com, as well as a gallery of Live.com gadgets submitted by the community. Fun stuff!