The difference between this site and the Gawker Stalker is that:
- you'll be able to upload your own photos
- photos (and sightings without photos) will be mapped in real time (lag will be 1-2 minutes)
- photos and sightings will be tweeted as they are added to the map
- you'll be able to map any location which can be mapped by Google maps, so you're not restricted to Manhattan etc
- if your phone is email-capable, you'll be able to shoot a photo and upload it to the site immediately, giving real time feedback
I should add that, for the beta, you won't need to post photos of celebrities in your neighbourhood. This is more about testing the functionality of the site than trying to get any specific content.