Edit: I guess maybe the advantage of this design is that you can easily send the bill for everyone at the table to everyone (probably wouldn't fit into 140 chars), which eliminates the need for the user to individually choose which contact corresponds to which column of the bill.
If you implemented your own shout url generation you could just name the image with the short url and stop giving bit.ly that kind of insight into your operation.
Nice way to briefly hit the front page of Hacker News though, and the app looks nice!
In the example you gave elsewhere, the image would be http://billr.s3.amazonaws.com/J7W5uY instead of http://billr.s3.amazonaws.com/01C03E08-4CFD-4709-87C9-BB60FD... - so bit.ly wouldn't be needed.
The suggestion elsewhere in this discussion to encode the entire bill in the url is probably the optimal solution though. With a bit of caching it's probably the cheapest you could run your system (sans S3).
other than url shortening, does anyone offer this as a service? a key value only online service?
MongoLab has a nice one http://support.mongolab.com/entries/20433053-rest-api-for-mo...
That will return a json object as the value.