I've recently been working on a workstation that is running, GASP, Windows Vista.
While the circumstances surrounding my use of this machine have been pleasant, use of the machine itself is most definitely not pleasant.
I'm hoping to stop using this workstation as-is very soon, and instead install Ubuntu and run Windows Vista (or better yet, Windows 7) as a kqemu virtual machine within Ubuntu.
The main reason why I'd continue using Windows at all is because of a nifty program the office uses called Autotask. When I heard it was dependent upon Microsoft Internet Explorer, I though for sure it would be a disappointment, but I'm actually very impressed. The software is incredibly well thought out and sophisticated in its functionality and information architecture. However, it does has significant drawbacks in the usability department, even despite having to use MSIE.
For example, almost every link opens a new browser window. This nearly drove me crazy until a very good Samaritan informed me that using Firefox and "IE tab" would allow Autotask to operate within Firefox, and just as importantly, open "new windows" within tabs instead of popups.