We've just finished a project using Caliburn.Micro: http://caliburnmicro.codeplex.com/
It's pretty easy to use and nice a light. We also used MEF as the IOC container, had to do a couple of things (on the server side) that it didn't do out of the box (unless I missed them), such as spinning up our WCF services and all of their dependencies, and was a little hard to diagnose when we had some dependency issues - but we did have some code that we were running on our build server that told us we had them. But overall MEF + Caliburn was a very nice experience. Neil.
