As Cult of Mac notes, the default behaviour for touchpad scrolling in OS X Lion is reversed. In previous versions of OS X, you move your fingers down on the trackpad to scroll down. In Lion, you move your fingers up.
The reason for this is probably to match the behaviour of iOS, where you “push” up on screen to scroll up.
So why is this wrong? Simple: when you touch a screen, cognitively you’re directly manipulating what’s on it. Your brain expects what’s under your finger to move in the direction you push it or drag it. It’s mimicking the way that real-world objects behave.
When you move your finger on a trackpad though, you’re not directly manipulating what’s on screen – you’re manipulating it at one stage removed. There’s a cognitive dissonance to be overcome before it feels right, reinforced by the 20+ years of scroll wheel behaviour doing the exact opposite.
I hope that Apple makes this behaviour optional – because it makes about as much sense as having a single button on your mouse.