I think this is a fair enough thread and a legitimate question.
Before I got a Cube, my only experience with a Mac was the ones setup at CompUSA or Frys, we didn't have a local Apple Store then. I'd pass them, play around with them for a bit and came to the conclusion that with OS X, they were tediously slow. The Dock would catch/freeze, windows would resize terribly slow and sporadically, applications would take what seemed forever to launch, loading and scrolling web pages with IE was a joke and the viewing PDF files was next to impossible. Now this is when OS X first came out and as much as I wanted to love it, I just couldn't. It was beautiful but severely flawed in my opinion.
Keep in mind spending 10 minutes with a machine that feels terribly slow compared to Windows performance wise is no measure of the productivity value between the two. That in which I believe OS X wins hands down.
Those who stuck with OS X in it's early days are truly the loyalist of Mac users. I know though many didn't, and even when the new Macs shipped with X, many would never boot into it. So it wasn't just the opinion of Windows users that OS X was some what unuseable.
OS X.1 has improved leaps and bounds over X. Everything has been speed up ten fold but even with newer hardware such as my PB 667 DVI, it still feels as if I'm fighting the GUI at times. Window resizing is still a little jerky and browsing PDF files is not exactly quick.
With Jaguar's Quartz Extreme hardware acceleration, I think a lot of speed issues concerning Aqua will be coming to an end. From what I've heard, even those without 3D accelerated video cards will benefit greatly over X.1.
Is OS X as fast as Windows on comparable hardware? No, not even close. Does it hold potential to be as fast as Windows or other GUIs? Absolutely.
As for the human eye not being able to perceive more than 24-30 FPS, that is a misconception. It is believed the human eye can see some where around 200 FPS. The misconception lies in that theatre movies are displayed at 24 FPS and TV at 30. The reason this seems normal is due to motion blur. It gives the effect that the picture is moving faster and more fluidly than it actually is. Computer video games can not reproduce that affect. That's why 24 FPS seems slow and fragmented compared to 60 or 100.