I also have witnessed the same problem recently. Not too long ago, I switched from a Droid Incredible to an iPhone 4S and have been nothing but completely satisfied. I have had many times where I have actually tried to run my battery completely dead so I can get a full recharge, as this is recommended to keep your battery in shape to hold a better charge. However, I will admit that it is truly hard to run your battery dead in an iPhone 4S in a complete day.
I usually start using mine at 8:30 in the morning and often times dont stop using it until 2:00 am, a full 18 hours after that, and I do use apps on my phone all day long. This phone simply has awesome battery power and that is a definite plus that I am okay with!
However, I came up to visit New York this week and I have been charging it off of my MBP because it has allowed me to keep my phone closer to my bed. However, I have noticed the next day that with the charge from the MacBook Pro, my battery doesn't hold its power near even half as much as it does when I charge it every night from the wall charge.
I will say that I have noticed an extreme difference in battery life with charging in a wall vs. charging from the MBP. I would highly recommend charging solely form the wall unless you absolutely have to charge from your computer, as I have noticed that this keeps your battery charged for MUCH longer.
Hope this helps with your question.