Marco Arment:
You can find friends through your linked Facebook or Twitter accounts, your email addresses in Contacts (from the app), or by entering their email addresses yourself (on the website). Since we’re starting from zero, check back often over the coming weeks to find more friends who linked their Facebook or Twitter accounts with Instapaper.
This is a great update to one of the best apps and services I have used in the past 3+ years. This update is worth $20, but will cost you nothing — amazing.