I really hate using windows. Is it Viruses or its speed? May be I am biased. One reason is expectation since it get so much from users. When something goes wrong on windows it really get on my nerves, each second I lost becomes hour. On Linux things are different because I enjoy experimenting things on it. Things always take time here like I have seen people spending days for installing some software on Linux ending up learn to live without it.
Windows is necessity because of game. My worst experiences on Windows are setting the PATH variable, deleting file which operating system claims to be used by something even just after restart it says so, then comes the speed if you are not formatting/fragmenting the disk or cleaning registry it really becomes slow after 5 to 6 months of use then searching, starting and shutting down takes a lot of time. Actually Windows help you here so it keep on crashing on regular intervals.
Once I have spent 2 hours on running a java program which uses oracle jdbc driver, I have set it in path variable but not restarted the dos window(my fault :P).
Sometime it decides not to end a program it doesn’t matter what utility you use. Then comes problem while deleting sometime also copying files/folders which it claims to been used damm .. I have shut all processes except system critical processes still it is been used. Once a friend comes to me with a folder on his desktop which he is not able to delete because it says the path does not exists. The folder is empty and it is on his desktop. We tried some third party software to delete it which after restarting the computer says the same thing(no folder with this path).. Finally he has to reinstall Vista.
Then there is the amazing so called user friendly user-interface! and icons in shell32. With os comes ridicules themes which consumes reasonable resources the old classic theme is still on top. If you are a mac user it seems like ages old interface.Microsoft is successful only because people are stuck with it and some good software specially games run on their os only.