Windows 7
The part of the internet who's not yet apathetic about Microsoft's announcements is happily blathering about the new features. Well it's interesting enough - in my opinion - that the inclusion of options for the user to switch annoying notifications off has to be considered a feature...
Also, it might be just me, but the new taskbar reminds me of KDE's (especially KDE 4's) a great deal. Also it's hard not to notice that with the Libraries added the folder view is increasingly reminiscent that of OS X's. I'm quite sure Steve won't fail to mention it in the next Keynote.
Not passing judgement here, just saying. It'll be interesting to see by the time W7 ships (promised 2011) how linux desktop systems and Mac OS would look.