My battery life seems tons better than it was before. But who knows, maybe I had some crappy rom that said it was using a single core but it was really wasting battery by enabling the second one at all times.
All I know is I was reading on my phone for about an hour this morning and it was still at 92%.
Other than that, I'm pretty surprised with how well it's running. Sense 3.6 is ok, a little jarring to see some of the sense colors go out of the way for real ICS stuff (like when you're attaching a google account).
One thing I don't like is how they ruined the default app behavior. Before if you clicked a link from a twitter app, it asked what application to use. That's ok, you can change that particular thing from the default apps settings (and ICS Browser + destroys the default Sense browser), but if I'm in an email and I click a twitter name, it just goes straight to the browser. Previously it popped up a menu for a browser or twitter apps, and I'd rather have it go right to the app.