I've heard about some widgets using more power than it's supposed to save. In my case, I use advanced task manager and the auto kill works nicely. The auto kill enabled and apn disabled, My phone uses about 8% in 1 day.
Anyway I also noticed that with apn and background data enabled, the phone is warmer and eats battery power. This isn't the case when apn is enabled but background data is disabled. So I reckon it might be some software issue...