As someone who has been lucky enough to spend the last few months testing iOS 5 in various beta stages, it has to be said that the version we're all currently enjoying has come a long way since the early days.
When Apple released the iOS 5 GM not that long ago, I instantly noticed that my iPhone 4's battery life was lasting roughly half of what it was before. A coincidence, I thought. It'll sort itself out, I presumed. After getting the iPhone 4S, the problem persisted. Twitter and forums on the web over lit up with similar problems, and a few fixes were suggested, mostly to no avail.
There may be light at the end of the tunnel. Switching one little toggle in iOS 5's Settings app may hold the key to curing your iPhone 4S battery...