It has some incredible sample content including Iron Python language integration and WinForms Designer integration. By examining the Iron Python source code (not included in the SDK, but free at download center) you can see how a language can integration into VS in a rich deep way.

Updates include changes to VSTS Samples for RTM compatibility and signing of VSTA bits; DSL Tools remains unchanged since the Jan CTP. New samples include Editor Reference sample in both C# and C++, CustomSearchProvider ( C#) and RegExLanguageService ( C# ), and continued improvements to the IronPython end-end language integration sample with much better Winform Designer integration. New MPF sources; adding to the source for Package.Project the SDK now includes the source for Package.Shell and Package.LanguageService.

You can download the software at the VSIP site (login required).