I've been working with the Visual Studio Orcas CTP from March 2007 for a few days now. My focus had been around WCF and WPF and ensuring my CSLA .NET 3.0 development worked in the new CTP.
Then earlier today I tried building a workflow. And the workflow designer wouldn't open. Instead I got a concise little error dialog saying "Microsoft.VisualStudio.Shell.WindowPane.GetService(System.Type)". This was the case with both C# and VB projects.
Worse, attempting to close VS after that point caused a complete VS crash. It turns out that other designers (like project properties) fail as well, with similar errors.
In talking to some people at Microsoft, I discovered that the problem wasn't universal. But in talking to more people, the root of the issue appeared.
I downloaded the huge 9 part VSTS/TFS edition of the Orcas VPC. Other people downloaded the smaller 7 part VSTS-only edition. The problem only occurs in the big 9 parter, and is due to a side-by-side issue. Some VS 2005 components are in the bigger VPC to support SQL Server, and they are causing the issue. The 7 part VPC doesn't have that functionality, or those components, and so the SxS problem doesn't occur.
So I'm about 80% done downloading the 7 parter, then I can get back to work.