Very clever! I think this is a great idea. There's a startup here in the Seattle area (http://www.glympse.com/) that's doing something similar, but—frankly—I think I feel a lot more comfortable with your model, especially since I think usage is a lot more likely (and abuse far less likely) in a 'pull' scenario like this one.

Good job!

Also, I have some 'constructive' feedback. Please note that I really do think your app is cool, and I'm only trying to help you make it better:

- whru.at should give me the option of typing in my location, or manually locating myself on the map.

- whru.at and Space-time are very different names. Which one do you want to use? (personally I like the 'texty' domain name better)

- It looks like you're using Titanium or something similar to build the UI. Kill this, and move to Objective C. The selection highlights on your table view are weird.

- Please only use system fonts.

- Only use pull to refresh or a refresh button, and not both.

- The color scheme seems to be all over the place: black, white, orange, blue, gray... Check out appdesignvault.com, or other similar resources for pre-built iOS app themes.