I have loaded Apple’s Lion (10.7) on several machines so far. One of them uses a basic USB scroll mouse while the others are using Magic Mice.
For several minutes, I thought I was losing my mind as I attempted to scroll some pages on a web site. The scroll action of the USB mouse is opposite of what it is on the Magic Mice (and opposite of what it had been in Snow Leopard).
If the “Move content in the direction of the finger movement when scrolling or navigating” box is checked, moving the scroll wheel towards the top of the mouse moves the page down. If it is not checked, this same action moves the page up. To return to the original scrolling behavior, uncheck that box.
In order to even see the configuration screen above, you have to disconnect your Magic Mouse. It is located under Settings->Mouse. It does seem rather odd that you can’t configure a USB mouse if a Magic Mouse is connected. On several systems, I do leave a basic USB mouse attached. It makes it much easier to reconnect Bluetooth devices after battery changes. As you can see from the configuration screen, you are offered a chance to set up a Bluetooth Mouse, but from that screen, there is no way to configure a USB mouse directly.