hear of Vs hear about

To hear of something is to become aware of it, whereas to hear about something is to be informed about it, for example, to receive news about it:

Have you heard of John Key? [i.e. do you know who John Key is?]

Have you heard about John Key? [i.e. have you heard the news involving John Key?]

I heard of a new restaurant in the Gaslamp Quarter. [i.e. I have learned that there is a new restaurant.]

I heard about a new restaurant in the Gaslamp Quarter. [i.e. somebody told me about a new restaurant (and she wouldn't shut up about it for three trolley stops).]

A similar distinction exists with knowing of and knowing about, telling of / telling about, and similar pairs of verbs about information transmission.