Retrievr provides an interesting way to search and browse Flickr. You sketch out what you want to see and it tries to make a match. Results tend to vary a bit.
In my experience, the results are usually fairly good, sometimes even stunning - considering the artistic sophistication most of us are able to come up with (gallery forthcoming); and in the cases they're not so stellar, they are at least entertaining ;-) But clearly, the approach has its limits.
What it lacks in accuracy it makes up for in fun. Thanks Peter.