Ever use autofill in Safari only to have it fill in the wrong information? For example, you might want to use your work e-mail address, but it always chooses your home e-mail address, or you want it to fill in your cell phone number, but it always chooses your work number. Unfortunately, there is no way to tell the System which bit of information is “primary”.
I just released a free app on my website called Safari Autofill Prefs that will let you choose the data Safari should use when doing an autofill.
FYI, Safari uses data from the Address Book, specifically your “Me” card. You can check this data by opening Address Book, then going to the Card menu and choosing Go To My Card. If it brings you to the wrong card (or no card at all), find your name, then go to the Card menu and choose Make This My Card.
Once you’ve located your “Me” card, make sure all of your various addresses, phone numbers, and e-mail addresses are entered, then try Safari Autofill Prefs to pick the items that Safari should use.