Personally,I do not think 5.1 increased anyone's battery life substantially. From what I can tell, Apple seemed to have made adjustments for when the phone is in standby, reducing drain at idle.
There are examples of people going a day or two without charging, showing high usage and having excellent battery life remaining since, the update.
However, the key is, how is the device being used? If I use my iPhone strictly to playback music guess what, I can show extremely high usage and can easily go almost two days before having to charge again. Conversely, if I use my iPhone primarily for making calls and a little surfing, with a usage of around 5 hours then, you can bet the battery will be almost fully depleted (by days end). I would factor in a reasonable standby time of 12 hours to be fair. But not even close to a day or more. This I think is more the norm.
I feel the overwhelming majority of people under mixed usage, calls, email, surfing, messaging, facebooking, tweeting, etc will get through most of the day (14 hours?)) before having to charge.
Again, I feel Apple tweaked the idle drain, and not, specifically, the phones features. For example, if the talk time for the phone was 8 hours (on 5.0.1), I do not think the update (5.1) made it 9 hours so on and so forth.
To really know if battery life changed dramatically (as proclaimed by some), a controlled test would have to be done. Two phones with the different softwares being utilized exactly the same way. That's the only way of knowing for sure.
This is solely my take on things...