Just registered, looking forward to seeing how this will be used. A free, legally admissible (still skeptical of that point) service like this is sure to tip the scales in favor of individual inventors and innovators at least somewhat - which is always a good thing (let's pretend the U.S. throw money at people to win "legal" system doesn't exist).
I think it just hashes whatever it is, and transmits a minimum of BTC to that hashed address on the blockchain. You can do this yourself for free with any bitcoin client.
Subsequently, that transaction is encoded into the blockchain forever, and could be pointed to in a court of law.