I have several forms in a C# application. I use Visual Studio 2010 Beta, but .NET 3.5 and C# 3.
I have a base form, called FilteredQueryViewForm in the Shd namespace
I think you meant that your Form1.cs[design] didn't update when you added your base class. I had the same problem. Strangely enough, the program will run just fine when you press start, and you'll see your base class components on your Form when you run it, but not when you're in edit mode.
Just double click Form1.cs on the solution explorer. It worked for me.