Ask HN: What are your favorite techniques for driving viral growth of a website?The essence of viral marketing is making one customer sell to the other.Here are some well-known examples:1) Photo-tagging on facebook. Tagging is the primary means by which photos are made social: when a user uploads a photo, they can “tag” their friends who appear in the photo. Notifications are sent to tagged friends letting them know that a new tagged photo of them exists on Facebook, and feed stories are published on both the tagger’s and taggee’s profiles.Users who receive a notification that they have just been tagged usually investigate the photo. If they don’t want to be associated with the picture, they “detag” themselves from it. Similarly, users who see a feed story about their friends being tagged in photos often check out the photo.2) Asking a new user for permission to automatically send invites to all of their GMail contacts. When you register for twitter, you have the option of allowing twitter to automatically log-in to your GMail account and send out invites to all o