When I add a photo to my favorites, as most of you might do, I check his/her photos and add the member to my contacts if I find their photos interesting. Flickr emails me a daily digest of my contacts new photos. Nice!
I always find favorites of my contacts fascinating. I sometime add another contact from their favorites. I checked their favorites from time to time until I found a great Flickr hack using Yahoo! Pipes, which makes it possible to subscribe to a RSS feed of the latest photos marked as favorites by your contacts. Fantastic!
I think his pipe is one of the most complicated ones and I have leant a lot from it. I wish I can give ratings on pipes.
We should not forget that the comprehensive Flickr API made the hack possible.