I have used mac address to identify iOS devices in server side. When run my application with iOS 7 unable to retrieve the correct mac address. Alternately i used
NSUUID *oNSUUID = [[UIDevice currentDevice] identifierForVendor];
[strApplicationUUID setString:[oNSUUID UUIDString]];
You can no longer get a unique ID per device.
identifierForVendor is the best you're going to get. Apple has systematically disabled identifying a specific device so that users' IDs can't be passed around by marketers.