Many consistent testimonies makes us believe that the 2.2 firmawre of the iPhone tends to reduce the battery life by 20 to 30%. It seems that for an unknown reason the device consumes much more power while sleeping, and sometimes even becomes hot.
If the drop of battery life was not enough, we have also noted at least on one occasion that the telephone became hot at the bottom a pocket while at the same time any synchonisation or Push function was disabled.
[translation by crispin]