Hi
A few days ago MEF
Preview 5 was released on codeplex with all the source code, docs, test
and samples developers need to get started. MEF will be a core part of
.NET Framework 4.0, These preview releases available so folks can use
MEF on Top of Dot Net framework 3.5.
You can read more about it here.
http://codebetter.com/blogs/glenn.block/archive/2009/04/11/mef-preview-5-changes-and-enhancements.aspx
Vikram