I am interested in finding out if you are finding any major performance issues with Class Designer - especially in creating new diagrams or opening existing diagrams. Currently the time taken depends on the size of the project (and of course on your CPU speed, memory etc.) as we parse the code files in the project the first time a diagram is created for a project.
When we compare ourselves to the existing UML tools in the market we are doing as well or a lot faster. However, when you compare it with WinForms we don't do so well. : )