Have you checked out the Mix Sandbox in the Sky yet? It is a free web hoster that has all the cool bits we are talking about here already installed.
If you are here at Mix, it allows you to build, install and share YOUR work. If you are following the action from home, you can see what folks are building.
Notice it is just a demo, so not everything fully works… You will need the beta of Silverlight 1.0 that we just released (silverlight.net)