It's not just the speed, but the stupid low priority Windows gives to screen refreshes and user interaction. Say, you click on something and a popup window appears. The window should be drawn as fast as possible, then do whatever stuff that has to be done in the background. Instead, the window half-draws, appears to freeze for a few seconds, then finally finishes drawing. This is completely unacceptable in a 2005 operating system running on a 3-4Ghz computer with tons of RAM.
But this is just a minor annoyance compared to the much larger design flaws in Windows. Who could ever think the Registry is a good thing?? (although makers of spyware seem to like it) And what about configuration changes that mysteriously go back to MS defaults after a random amount of time? And the bugs! I started to list whenever I found a bug that I could reproduce - and I now have a list of over 500 bugs! I have to use this crap at work, but I certainly will not have a Microsoft product in my home!