A video has been posted by etradesupply on youtube which shows a iPhone 5 back cover.
There is no guarantee that this is true but assuming this is we see some significant changes.
2.Headphones jack now at the bottom and not at the top.
4.Bigger and maybe louder speakers.
5.Metal body instead of glass.
Via - Cydiablog
3. iOS 6 rumors
4. Apple WWDC