If you ask me, it's most definitely screen time + cell radio. I've had mine for 2 days now. 1st day I was astounded at how long the battery lasted. As others mentioned, it wasn't long before I began to put "my apps" back on using Titanium Backup. After fiddling with the discrepancies between GB and ICS, and getting the proper versions of my apps back...I noticed quite a drop in battery life. Primarily when I'm at work. I have 1-3 bars sometimes, and other times absolutely nothing (I.E. it's searching for 3G, we have no LTE here yet). That said, my old Evo had the same behavior, so at least I can say it's not a crappy cell radio in the unit. If anything, it's better. It DOES, however, definitely use more battery to power it. I've found no way to tell the phone to differentiate between 3G and searching for LTE, so I assume that isn't really the problem. I've got 8h 0m on battery, with 29% of use being screen time, 27% Cell Standby, and 12% voice calls (I made one call for about 30min over lunch, and received one that lasted MAYBE 2-3min prior). I'm sitting on 35% battery right now. To me that is....meh. Not terrible, but definitely not great. Screen-on time is 1h 5m.
EDIT: I never have GPS on, unless I'm going to use it. I never use BT. Also, I can't get on WiFi at work, so that is why the in-depth explanation of my 3G woes above.