When the iPhone 4S was released, people wondered why the new iPhone didn't support 4G. The answer is, apparently, that it does, it just wasn't enabled in software. This new update enables 4G support under AT&T. Along with that support comes absolutely abysmal battery life. Since running the update, my phone is now a little pocket-warmer. Three hours after my phone was charged to 100% after updating, my pocket is nearly on fire and the battery is now 50%. So I went looking for a way to disable 4G. You can't. I had to disable cellular data entirely.
But wait, there's more! Does the 4S really do 4G? Nope! It just lies about it.
Which means that the battery issue is apparently a new bug, entirely unrelated to lying about 4G, since the only actual change is that the iPhone 4S claims 4G under AT&T despite the fact that it's using the same 3G connection it's always used.
Of course, iOS 5.1 also claims to contain battery-life fixes that plagued the original iPhone 4S launch. Whoops.