Microsoft is touting the same thing for their next version of windows. They say it'll be more streamlined and perform better than Vista.
You have to understand what is under the hood for both companies in their next OS versions to understand the differences.
In synthetic benchmarks Windows 7 will not surpass XP for raw system performance until there are at least 32 real or virtual CPU cores available to send instructions to.
Additionally Windows 7 still will not jettison the .dll/registry structure that severely affects Windows boot up times, clean up, etc.
Windows 7 will also likely be just as vulnerable to attack as previous versions which leaves users forced to run performance affecting virus/trojan/spyware checkers on top of the OS. Windows is so vulnerable, in fact, that the OS actually nags you constantly if you do NOT run a virus scanner.
A good deal of what Windows 7 is doing are UI improvements to try to leap frog OS X. You'll notice that Windows 7 adds a "dock" similar to what Tiger/Leopard have had for years. It will also add touch screen support, improved driver configuration and support, etc.
Snow Leopard is going in a different direction. Instead of adding lots of new features it is a top to bottom 64 bit re-vamp of the OS that should jettison the 32 bit pieces of the OS that are still there (32 bit apps will still run though, presumably in a virtual space with limited memory, etc).
The two key technologies that the new OS X load will have are Grand Central, which appears to be a way for programmers to lean on the OS itself to handle mult-cpu threading and Open CL which is going to enable some use of the GPU(s) by the system software.
These are much more "game changing" technologies than what Windows 7 aims to do, but naturally only time will tell on how effective they are... I would say though that hopes are very high that the bar will be set very, very high for system performance with the new Snow Leopard load.
I should point out though that Windows 7
will have native OS level support for
Blu-Ray. Apple needs to pull their heads out on this one before they look like idiots.