I don't know what the big deal is. I agree that scrolling in the browser is not at smooth. iPhone wins hands down. Not just over the N900, but Android too.
But other than Ovi Maps I think the Maemo UI is quite fast, and very pretty. So they put all their effort in fluid scrolling What's the big mystery again?
I am a Mac user and love OSX. But I do not want an iPhone at all..I think the lower resolution is awful. I am still stunned by the crisp text on the N900.