Pablo Galiano, from Clarius, has produced some nice content explaining the Visual Studio 10 extensibility, which is based on the notion of VSIX, and also uses a lot MEF.
He gives some links MEF, and presents the Microsoft.VisualStudio.ComponentModelHost
MEF and VS10 beta 1
VS 10 beta 1 extensibility model (Part 1)
VS 10 beta 1 extensibility model (Part 2)
He explains why the F5 experience (Debug or Run without debugging) is much quicker than in VS2008, based on the notion of extensions, and details the Extensions folders, and registry hive
VS10 beta 1 - the Microsoft.VsSDK.targets revisited
VS10 beta 1 - User extensions versus Trusted extensions
VS10 beta 1 - No more Devenv /Setup
VS10 beta 1 How do I hide an extension
Deploying a VSIX as a trusted extension
VS10 beta 1 The registry hives
He explains how the VSIX manifest has counterparts in the new project dialog
VS 10 beta 1 The new project dialog
He explains that the exact same mechanism is used both by the F5 experience and the deployment
Deploying a VSIX from a MSI (using Wix)
Many of you will be relieved to know that there is no longer any PLK
VS10 beta 1- No more PLKs
Pablo finally explains how MEF can be used to extend packages.
VS 10 beta 1 Exporting MEF parts from a VS Package (part 1)
VS 10 beta 1 Exporting MEF parts from a VS Package (part 2)
VS 10 beta 1 Exporting MEF parts from a VS Package (part 3)
He also created a new site in the Code Gallery (http://code.msdn.microsoft.com/VS10XSamples) that he uses to centralize all the samples he has been creating.