You probably know that Apple's Address Book lets you create "Groups" of people, and you might also know that a given person can be in multiple groups. For example, you might have a Family group, a Soccer Team group, and a Christmas Card group, and your brother might be in all three of them. That's pretty neat, but unless you have an incredible memory there's no way you're going to remember which groups your brother is in. And there's no indication in the Address Book that a given person is in any group at all, let alone an indication of which one(s).

Unless of course you hold down the Option key. Of course.

In the picture below I've found a person's card, clicked on it in the "Name" column, and then held down the Option key. That produces the yellow highlighting, letting me know in an instant that Mom is in the "Mass email list" group, the "test group" group, and the "California" group. Let's face it, that's pretty cool.


And that's four.