TweakTown compared the CPU and memory performance of Windows 7. Here's a taster:

When it comes to having a look at pure CPU performance, it seems that Windows 7 isn't quite as efficient as Windows Vista. As for memory, though, there isn't a whole lot of difference. On the down side you're not going to be breaking any wPrime records under Windows 7 for the moment.

On the other hand, while the CPU scores are lower, when it comes to graphics card performance we can tell from our previous articles that Windows 7 does a good job of keeping up with the older and more mature operating system; it coming out in front at times and sometimes falling slightly back.

What we're seeing today doesn't turn us off Windows 7 one bit. Once a bit of time has gone past there's no doubt we'll see CPU performance come up to or overtake that of Windows Vista. This should also result in slightly better graphics card numbers and anything else that benefits from more CPU power.

There's no reason to not be excited about Windows 7; it's the upgrade that Vista probably should have been. With that said, though, if Vista hadn't existed, then it's possible that W7 wouldn't be as good as it is now.