Usually I'm for the - if it does the job, I don't care which OS it is. However, my recent two annoyances with Windows:
1. why for the love of everything do I need administrator permissions to start a simple user application, for example a book keeping program? Why do user applications even get those options? I try to maintain 2 office computers, but it's insane that every simple user application requires admin permissions.... Why can they be made that way? So theoretically I can put a password that protects the computer, but practically I need to hand out this password because she'll be unable to run the necessary programs.
2. Windows are a very untidy OS. F.e. Vista. Did you see that little hidden folder, in MyDocuments, named AppData? It had more than 20GB of files in it, saving parts of each and every single program that was installed since the first boot of the computer. And yes, I did run various cleaning programs regularly.