i can successfully say there is LTE in the Dearborn (southfield freeway), Melvindale, Allen Park area and even a little pop up in Westland and it is indeed fast. i loved every minute of using 4G on my S3
a friend of mines got an LTE signal in Ypsilanti on his iPhone 5 and there have been several pockets of LTE signals on the eastside of Detroit, Eastpointe, Warren. so hopefully we'll see more soon