Browsing my webserver access statistics I found an interesting bot entry and followed it to the website http://iconsurf.com/. IconSurf seems to be a nice project to gather favicons. It creates unique hashes of all this little images to compare them with hashes already stored in the database. This feature allows to check if a favicon is used twice or even more.
Besides that it’s of course a hard way to visually compare all these icons.
»This website is intended as a resource for webmasters, consumers, and surfers. The icons displayed here are the favicon.ico files from a variety of websites. By clicking on any one icon you will be directed to the website which hosts the icon.«