I wanted to put that in the title but it is limited to 100 chars. On their blog over the last year they've mentioned some neat looking OCaml tools they've written (some have been open sourced)
I particularly appreciate their approach to data storage and security: http://skydeck.com/security/ ... no need to store this server-side where it's out of the users' control.
I cannot even imagine there being valuable information in my cell phone bill. But, no one would spend months building a business around the idea if there was really nothing there, right?