Well, Windows 7 is here to stay. Really useful, more intuitive, not as nice looking yet as OS X, neither as sleek as Ubuntu, but overall a very good Operating System (OS) indeed.
The best of course is that it is a true 64 bit OS, which makes it faster and more secure than its previous siblings.
However, despite Windows XP being the most popular OS ever, there was once (and still is in operation, on high-end workstations) the best OS MS ever released; it is still a mystery why MS stopped bettering it and opposed to continuing to push adoption and third party development for this particular OS. I'm referring to Windows XP 64 bit (wrongly labeled sometimes as x64).
It is flawless. It was the fastest OS there was when it was released, save for a few Linux distros that truth be told did not have a very good network support. On AutoCAD and similar packages you could really appreciate the advantages of XP 64 vs, 32 bit. In fact, not only architects and designers benefited from it, some of the animated movie pictures released a few years ago were crafted on machines based on this.
Too bad MS decided to stop releasing even Service Packs for it. It will retire support soon too; so those of us that have a computer running it, are a little bit sad yet grateful for the eXPerience. Windows XP 64 bit has been the absolute best OS released ever by MS before Windows 7 64 bit.
Time to upgrade it to Windows 7 now.