When I use Resharper's auto optimization (Ctrl-Alt-F) on a WinForm that has been converted from a VS2003 solution to VS2005, it often breaks the designer, thus making the Form unusable.
It seems that the problem is with converted forms only, because they have the generated InitializeComponent() method inside the (only) form class file, unlike forms created in VS2005, where a partial file is used for the generated section.
To reproduce, create a C# form in VS2003, add some controls to it from the designer, save, and then open in VS2005 (it'll be converted). Then open the form source code, and optimize everything using resharper (Ctrl-Alt-F, select all options, OK). Trying to open the designer now results in exceptions.