I take my Flickr favorites very seriously. Looking at people's photos and their favorites I think you can get a pretty good read on them (this guy really like cats and boobies!). I find it especially fascinating when someone takes really interesting pictures but has really boring favorites (where as I think I have really cool favorites and not the most interesting photos).

I love going through people's photos and starring a bunch of pictures I like and then looking at my favorites page for interesting patterns. There'll be stretches of cool or warm photos or interesting juxtapositions like these two; marked as favorites back-to-back by pure chance: