I've used the Windows Live Expo beta to get rid of some left over construction materials I had as well as to sell the Mariner's tickets I can't use, I have season ticket in the Terrace Club. It is excellent and the new features outlined in this post should really take off. The integration with Spaces offers great value to both products. We should start seeing more stories like this one.
My hope is the Spaces people learn from this and start offering some of the same access control features that Expo has.