Geoloqi

Leave yourself a note which you'll get next time you're at the grocery store.
Get an SMS when you're nearby apartments that match your Craigslist search criteria.
Automatically check in to your favorite places on Foursquare if you're there more than 10 minutes.
Automatically send your carpool buddies an SMS when you're half a mile from the pickup spot.
Automatically send your boss an email if you're not at work at 9am saying exactly how late you'll be.
Update your AIM status with your current city.
Turn on lights when you get home, turn them off when you leave.
For developers: Trigger a callback URL when you enter or leave a specific location.