This project uses Google Social Graph API, an API that allows to work with public XFN information from webs.
This data is not real-time that can be gathered using Twitter API, instead when Google crawler indexes a Twitter web it searches for XFN data and collect it to be used with Social Graph API
Yes, but data is public and Google is crawling for it, so go and ask Google about it!
Write me a couple of lines: mikel at olasagasti dot info
Short answer: NO.
Large answer: NO. Whoistheleader.com uses public data that does not need you to login in Twitter.
For a normal average user all the connections gathered by Google are shown, but for big and large users only some of the connections are shown.
No. Whoistheleader.com is just a site created on my free time. The very little money earned from the banners is being used to pay part of the hosting at Linode. If extra money is earned it will be donated to FSFE and GNOME projects.