I clicked that yesterday and got a notification telling me that it would take a while to get the copy of the data. Still waiting. In the meantime, a user who clicks that button has to guess whether it's safe to delete their facebook while facebook is getting the data.
However, the facebook data isn't good enough because I found that most of my friends didn't put in their contact information. So whether you download a copy of the facebook data or not, you're going to lose contacts (you decide whether it matters) and the rest you're going to need to call friends of friends and find the contact info you need, or ask people directly on facebook for their information.
However, the facebook data isn't good enough because I found that most of my friends didn't put in their contact information. So whether you download a copy of the facebook data or not, you're going to lose contacts (you decide whether it matters) and the rest you're going to need to call friends of friends and find the contact info you need, or ask people directly on facebook for their information.