A current fascination of mine is the quantification of the internet. Tags allow pictures and words to be sorted like numbers. Google has turned this into a game with the Google Image Labeler where you compete with someone else on the inter-web to correctly label as many pictures as possible in 60 seconds... The result is a cataloged set of pictures and a more efficient search engine. Everyone is a winner.
Flickr has always been a great planning tool. You can get a glimpse into a person's life, see how they use a product, see where they live, who they hang out with, etc. The newest tool I've enjoyed using is the Flickr Camera Finder. It can sort most uploaded pictures by the camera that took the photo. This means you can sort photos, make charts and do all sorts of stuff with images. I've been thinking about buying a digital SLR, so this has become a favorite site of late (any suggestions on cameras btw?).
There is so much data scattered about the internet right now. This is an exciting time for people to categorize and organize everything out there. This is a topic I could talk hours on, but I must go. Here are two sites to keep you busy though: Marumushi Newsmap, a news aggregator I look at daily, and Popurls, an aggregator of aggregators.