Historically, in most desktop operating systems, rolling a mouse wheel or sliding your fingers on a trackpad has made the contents of your active window scroll in a consistent direction. Rolling the mouse downward (toward you) scrolled up, while rolling it upward (away from you) scrolled down. In Lion, this has been inverted so that rolling the wheel (or sliding your fingers on the trackpad) downward moves the content down, and rolling upward moves the content up.

The difference seems small, and once you develop the muscle memory that makes the page scroll the way you want it to, it shouldn't be a big deal. But if it's slowing you down and you just want to set it back to the way it was so you don't have to deal with the new functionality just yet, here's how to do it.

By default, enables what Apple's choosing to call "natural" mode, in which the content moves in the direction your finger is moving. To reverse it so that the scroll bars, rather than the content, follow your finger, uncheck the checkbox for Scroll direction: natural.

For my part, I'm going to keep giving the new, so-called natural scrolling direction a fair shake before and see how I like it. But if you're losing productivity to the novel scrolling direction, I don't see how anyone could blame you for setting it back the way it was.