networks have in common? It's a well integrated signup process that
connects you at the beginning with people in your address book that
are already using the service as well makes it seamless to invite
The downside is this technique has been criticized for being spammy.
So make sure users can opt out of sending emails.
The upside can be tremendous with thousands of people signing up
daily. The experience for each new user is also enhanced when they
are connected with more people they know.