I think you are expecting too much. Having to charge your iPhone every 12 hours on regular usage is quite magnificent. That's probably the best battery usage I have ever heard of.
You have to realize that smart phones need a lot of juice. They consume a lot of power no matter what. It's not like a standard cell phone. It has a bright display and UI that just needs the extra power to function properly.
If I were you......I would consider yourself "lucky" to have an iPhone 4S that gets 12 hours regular usage. I'm lucky to get over 8. And that is about average for Any smart phone with such capabilities. Most Android phones get about 6-8 hours usage. So your really not doing too bad.
Why was it so good before? Well, most of the time, iPhones have pretty good battery right out of the box, as you set your settings, and collect data, add email accounts, etc it starts to use the processes it is suppose to to function properly. This is perfectly normal. However, if this is unacceptable to you, then I suggest you stay away from any smart phone with such capabilities. otherwise, it seems to me that you have significantly good battery performance. This is how smart phones are, whether they are Android, WinPhone7, Or the iPhone.
I truly jealous.
Hope this helps.