[ddaddy]

Let me tell you a little story about my Nokia.
I changed the product code so I can get an unbranded firmware.
I used Nokia Software Updater to get the latest unbranded firmware and all was great.
A month later I had a slight problem with phone and took it to the Nokia Repaird store. All they did was type my IMEI into their computer and it popped up telling them that I had changed the product code so it wasn't covered under warranty!! How did they know?!
Well when I did the softare update, my product code was sent to Nokia.

Apple could have easily implemented this. When you update or reflash your software using ITunes, it can easily send back to apple your IMEI number and a note saying you have it Jailbroken.
All they need is to check a database for your IMEI and they will know.

I dont know if they do this, but it is certainly possible for them and they are sure to start doing it.