Gizmodo has some info on how Windows 7 ought to be faster in ways that are, well, noticeable:
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.
This isn’t unlike Apple’s upcoming “Grand Central” software, at least in theory:
Grand Central takes full advantage by making all of Mac OS X multicore aware and optimizing it for allocating tasks across multiple cores and processors. Grand Central also makes it much easier for developers to create programs that squeeze every last drop of power from multicore systems.
The gist of all this programming is that software - for the first time, really - will be able to use all the hardware available in a system efficiently and smoothly, meaning current hardware should run better under Windows 7 and Snow Leopard when they arrive.