title: Finding friends through twitter, facebook, gmail, etc
body: <p>I have a web app, where I ask for a user's:</p>
  
  <ul>
  <li>Email address (required)</li>
  <li>First/Last name (optional)</li>
  <li>Twitter handle (optional)</li>
  </ul>
  
  <p>I'd like to allow them to find friends also using my service - if I understand correctly, I can offer the following methods:</p>
  
  <ul>
  <li>Given their email address, try to find their contacts. This may be based on their email provider. For example, if they're using gmail, I think gmail offers an api where I can search for a user's contacts. I take that list of email addresses, and check if any of them are also users on my site. </li>
  <li>If they supply their twitter handle, I can use the twitter API to get a list of users they are following.</li>
  <li>I can ask them to enable Facebook connect. If they connect, then I'll get their facebook ID. I can use this ID to fetch all their facebook friend IDs. I can check if any of those ids also match users on my site, that also setup facebook connect.</li>
  <li>Just a general search by first+last name.</li>
  </ul>
  
  <p>I think those are the basic ways for friend finding - am I missing anything obvious? I'm most curious about the gmail method - do any other email providers offer something similar, or is there some open standard for that?</p>
  
  <p>Thanks</p>