Layar, the (somewhat) augmented reality browser previously available only on Android, has hit the App Store. If it seemed cool on a G1, it's probably going to zoom at showing you what's nearby and where on a 3GS.
All the same features apply to the iPhone release. Choose your layers from sites like Wikipedia, Flickr and Twitter mashups, point your phone around you, and Layar brings up the results as blips on a planar, sonar-type screen, with a smidge of information about each one. You can tag favourite layers, grab screenshots, and get mapped directions to anything that seems just a tad too far to blindly walk toward. The best use case is finding food, services; at worst, you're probably going to lose some pocket cash on yet another coffee fix.
Layar is a free download for iPhone 3GS models running the 3.0 firmware.
Layar [iTunes Store (direct link)]