Paul Kehrer has developed an extension for Safari 5 called “ctrlSwitcher.” The extension let’s you use control or option + number keys to switch between tabs.
As a former Firefox user command + number key is a much more comfortable way of switching between tabs than Safari’s default keyboard shortcuts. I still would prefer being able to use command instead of control or option but extensions aren’t able to override previously bound commands because of security concerns.

The little bit of time that it takes to move my hand from the Magic Mouse to the keyboard and back again was driving me crazy. My web browsing has sped up considerably since I installed this extension.