This link has some good info about iCloud settings to help manage battery life. "The ability to automatically move data between your iOS device and the cloud is fabulous, but it can also deplete your battery in short order. " Managing battery life for iOS 5 devices | Macworld
I just got a 4S and am running it stock. I've got to say, compared to the Galaxy Nexus I had, the battery is phenomenal. It's great not having to worry about plugging your phone in all day.