A location-aware todo list. Today, I thought of something I'd like to buy next time I am at Wal-Mart. I know that if I put the words "tire gauge" in a note on my iPhone, there is a very slim chance of me actually looking at said note on my next shopping trip... But! What if there were an app that allowed you to add an item to your todo list with a GPS tag (added though the maps interface, perhaps? This app would then alert you when you get close to the tagged location, effectively reminding you to buy the tire guage. My question is, is this even feasible? Is the battery drain by the GPS too heavy to run in the background? Is there an API that could occasionally poll the GPS for your position and alert you accordingly? Hexck, does something like this already exist?