Google has put together a mobile app for its Android platform that allows users to search visually. Simply take a picture of something, and Google will compare it to the images on Google image search to try and identify it.
It can be used for all sorts of things - landmarks, books, game or record covers, contact info (where it'll employ text recognition), art and sculpture, certain places, like restaurants and local businesses, bottles of wine and company logos. Snapping each one will provide you with relevant information about the subject.
It's available now in the Android App Market for handsets running version 1.6 or above. Unfortunately, that doesn't include the HTC Hero, which remains defiantly 1.5, but has been promised an update to 2.0 imminently. Google has promised that the photo search app will roll out to other mobile platforms soon.