Can I reverse the scroll direction of my mouse?

You can change this in "System Preferences" -> "Mouse"

This change actually happened from Snow Leopard to Lion with the introduction of Natural Scrolling to match iOS scrolling behavior where the motion is expected to work on the content - not the scroll indicator - as the two move in opposite directions.

The system preference for scroll direction is all-or-nothing and applies to every input device uniformly. With some things, this just doesn't make sense. If you want fine-grained control of which input devices scroll in which way (for example, if you want touchpads to use the "natural" scrolling while having the scroll wheel use traditional scrolling), try ScrollReverser.