I usually switch my phone off overnight to charge, but every so often I will keep it on just so that I can monitor battery usage and wakelocks, just for peace of mind. Normally, my GS2 consumes between 1-4% overnight, but last night I had an email come through, and power went down by 13%. I could see the battery graph going along steadily almost flat initially as normal, then drop suddenly, obviously when the email came through. Its surprising the power those 2 LEDs consume! A handy feature in custom roms would be able to give BLN a time range, so you could switch it off through the early hours if required.