To get things rolling, let me start: Fuck Windows 7, a Vista on a diet which is really just the same stuff as before without all the clutter. Like Matt said, it is a glorified service pack at full retail price. Mac OS X Snow Leopard, despite Matt describing it as another glorified Service Pack, is not a service pack—even while it's surprising and inexpensively priced as a service pack.
The fact is that, while it doesn't include new eye candy, the new version of the Mac OS X operating system implements a full re-factoring of some of its core technologies (in software engineering, re-factoring means rewriting the code underneath but not changing the user interface.) Full 64-bit overhaul, completely new QuickTime system—which flies—a new Cocoa Finder—which flies too—and stuff like OpenCL and Grand Central dispatch, to name a few of the gigantic architectural changes. These changes are going to deeply affect—for the best—the performance of both the operating system and future applications, specially GCD and OpenCL. And all for $US29? I think we have a clear winner here, even while the user won't see new pretty icons. They just will see stuff moving faster than ever before.
So the way I see it is this: Apple got into a solid, fast, lean machine and retrofitted the engine to put it in overdrive. Microsoft, on the other side, just made the mess of Windows Vista actually usable with Windows 7. It will be a speed boost, yes, but only because the previous operating system was crap. So OS X wins again this round. Deal with that, Windows fanboys. [Image by Nep Smith via Cult of Mac]