The first few days I noticed a huge difference too.
Mine seemed to be related to the Data Network connection. I had the data radio on at work after the update and was receiving notices every time it dropped out of the network. Before the update I would not get notices. The screen turns on for each notice, the phone vibrates and needing to process a notice while also re-syncing with my email made me think they altered they data radio processing. I have my Data radio off currently and I'm still running 95-100% battery after 5 hours off the charger. My pre 1.3.1 percentage would be 70-80% at this time and my 1.3.1 with radio on was 50-60%
Just to clarify, I work in a steel reinforced concrete building. My phone stays in my pocket, which is under a metal desk for most of the day. So to say I was expecting any signal at work is a bit of a stretch.
My location services are off for days at a time.
Data Radio Toggle homebrew app:
http://www.precentral.net/homebrew-apps/data-toggle