Cheap Cost of Acquisition, indeed :). I have a feeling the ocean is about to get flooded with bottles from internet entrepreneurs trying to acquire users.

It's sad to say that my first thought was the marketing aspect of this, then I read some took 10 years to open. I don't think I could justify the response time to a client.

Hm, there are services that let you send a postcard from your mobile phone. How about sending a message in a bottle from your phone? :-)

That's a neat idea.