I just unboxed my iPhone 4S and restored it from a backup of my iPhone 4 and it doesn't have Siri on it. If you hold the home button it just goes to the old school voice control. Has anybody else had this problem?
Restore as new..don't restore from back up..I had this similar problem before on 3GS to iPhone 4 compass was gone on my iPhone 4..you are updated to the latest iTunes?
Also go to Location Services and make sure Siri is turned on so she knows where she is...
I restored from iphone4 iOS5 backup and had to switch Siri on as described above, as well as turn on location services for Siri (everything else was on).