One of the core principles in Flickr is having the ability to mark any photo that you see as being a favourite.
This page http://bighugelabs.com/flickr/surf.php from Big Huge Labs lets you explore this concept further. Choose a contact, one of your own or just a random person and it will display some of their favourite photos.
Click on one to see it large. It then joms to the owner of the large photo and shows you their favourites and so on, and so on and so on……..
This is such a simple concept and so addictive.
You have been warned !