This is a cool new idea. GPSNotifier for iPhone 4 ($1.99) sounds an alarm when you're in a specified location. It's an alarm based not on time but on where you are. Want to remember to pick up a specific item next time you're near a Walmart store? Set an alarm. Although a great concept, one limitation of the app is its granularity: it's limited by the number of cell phone towers in your area, such that you might only be able to specify that you're within one mile or more of the location you have in mind. Still, it could be quite useful.