if you are doing any kind of graphics programming using GDI+ then that is a dog. Although it is possible to get acceptable performance out of it with a lot of work, not game acceptable but good enough for light graphics work.
I'm doing some graphics browsing type stuff at the moment and the speed is more then acceptable for me in GDI+. In fact, I'm downright impressed. Way better than it's ever been using the raw Win32 API, MFC, or other software libraries.