I have loved using the MIUI Rom it has made my phone look pretty sweet. However I am taking the phone back and getting a new one. So how do I remove all the MIUI stuff and get it back to its original form?
Connect phone to PC via USB + Debugging, and run the RUU.exe. It will wipe everything and restore everything back to default including firmware, radio, HBoot, S-Off back to S-On etc.
There is no way they can tell you rooted you phone after a RUU restore.