UPDATE (4/5/2010): I uploaded a newer version with a few minor tweaks.  I finally created a screencast for this sample:

http://tinyurl.com/WpfMefStartupScreencast

UPDATE (2/27/2010): I uploaded a newer version of the sample.  I fixed some bugs and added support for loading a ResourceDictionary using MEF.  I will be recording a Ch. 9 screencast soon.

I keep on finding all sorts of fun and interesting uses for MEF.  I just threw together a sample for a customer showing how to use a splash screen + MEF to follow the “Make the application main window appear as soon as the user double-click on the application’s icon, when possible perform do all other initialization after.” principle describe here:

http://blogs.msdn.com/jgoldb/archive/2007/10/10/improving-wpf-applications-startup-time.aspx

I plan on explaining the sample in a coming blog post.  However, I wanted to share the sample without explanation as soon as possible.  Get it here:

http://tinyurl.com/WpfMefStartupTipsTricks

I used Visual Studio 2010 beta 2 / WPF4 for this.