We had them as address book entries on the back of people's badges at an O'Reilly conference I was just at. I saw people using them and I took one person's deta

We had them as address book entries on the back of people's badges at an O'Reilly conference I was just at. I saw people using them and I took one person's details in this way too. If I had to guess though, < 10% of people were using them.