Enter some comma-separated tags and the graph will show you what times of the year people have taken photos corresponding to those tags. Some queries I like are boletusedulis (scientific name of the porcini), morels, christmas, and bloodroot.
Each bar should be clickable, showing you photos from that day. Contributions from individual users are capped at 5 / date so the trigger happy and lazy taggers don't muck things up.
I felt like learning something about Protovis and I always like seeing seasonal trends in data, so I threw this together. It's not perfect (can't compare years, bars can be hard to click on), but hey, it works.
It loads 100 photos per page, so it may take some time to load photos and build the visualization. I also cap it at 50 pages of results. Do you really need to see more than 5000 photos worth of data?