I meant to post this a few days ago, but it fits in really nicely with our benchmark testing to explain what's going on under Windows 7's hood. Microsoft obviously focused a lot on the user experience in Windows 7, so a lot of work went into improving desktop responsiveness—smoothing out the little snags or hangs up that made people feel like Vista was too slow. Which is apparently a hard thing to do, since a million different things can cause slowdown. But the most frequent cause of hangups is a bottleneck caused by one graphics device interface application—an app that taps your graphics card—waiting on another GDI app that's being all slow and crappy.
In Vista, this could happen because the way the GDI was designed, a single app could hold a system-wide global lock, so apps running simultaneously constantly jockey for the lock in order to render on the screen, and if one asshole app doesn't let go, it screws every other app waiting in line. So Microsoft re-designed the way this stuff is orchestrated, so multiple apps can "reliably" render at the same time, meaning less bottlenecks. Besides improving reliability, the redesign actually improved performance with multiple GDI apps running simultaneously on multi-core processors, so you'll see real benefits from going multi-core, which no doubt makes Intel's Craig Barrett happy.
Oh yes, they also reduced the memory footprint, but anybody running Windows 7 already noticed this. So yes, Windows 7 really is more responsive, even if run-of-the-mill benchmarks can't exactly measure how that is. [Engineering Windows 7]