Flickr has made significant efforts at improving its mobile interface over the last year, and has just put out a useful update for iPhone and Android users which builds on that. Through the wonders of the latest iPhone firmware update, the built-in Safari browser can finally acquire the user's location information and pass it off to sites that request it. Google's Android platform has had this as well, but with both operating systems now supporting it, Flickr has gone ahead and added a pocket-sized version of its nearby photo viewer.
Now, whenever visiting the site you can view photos within a few blocks of where you are. Although unlike Flickr's main site, you can't see where each photo has been taken. Instead, it simply narrows you down into a general radius and shows thumbnails of the most recent ones.
I use this feature all the time on Flickr's main site which incidentally you can still use, and have it locate you from either phone's browser. However, I found this new version to do a far better job at narrowing down precisely where I was, as well as loading photos that were properly sized and optimized to stream in over the air.
I'm hoping future iterations of this will let you do some of the filtering and exploration you're able to do in the main site. I'd also like to see a pocket-sized version of Flickr's places pages which aggregate photos of landmarks and cities.