Thanks to Tim O'Reilly's twitter feed, I found out about this article explaining how the protocol used by Siri has been cracked.
First, the only surprise is that cracking Siri took as long as it did. Second, it does seem that while Apple tried to implement some security in the protocol, their implementation was still susceptible to a "man in the middle" style attack. Third, it's quite the interesting read in how developers/hackers/crackers go about the process of reverse-engineering a protocol in order to bust it wide open.
So, if you're technically inclined, there's enough information there to write your own app to utilize the Siri protocol.
The next interesting item will be seeing how Apple responds to this in order to lock it all back down again.