I'm on a CM9 nightly right now, and I also tried SlimROM 3.6 and I'm getting 12 hours out of my battery. I used CM 7.2 RC in between and got around 30 hours. That's probably what I'm going to go back to, just so I don't have to keep my phone on a charger at work and still be able ot make it through the commute + work day. Battery screen says 67% of my use is Android System.

Oh wow and all this time I thought the issue was that my battery was shot. I was seeing pretty similar results on all 4.0.3 based ROMs. Just flashed Gummy and my idle battery performance is much better. Was losing around 40% overnight on 4.0.3 (~7 hours), lost about 5% overnight on Gummy.

I can definitely confirm no adverse effects and an increase in battery life by turning off Google backup and removing the GoogleBackupTransport.apk.