I got mine yesterday at noon and beside plugging it in for the setup, I didn't really charge it so it was about 80% when I started using it.
I turned watch mode on pretty much right away. GPS is off.
With playing and plenty of notifications coming in (I get about 100 emails a day, about 50-60 texts and plenty of other notifications) and with heart monitoring on, I am still above 50% based on the little Icon on the Band itself, so it should easily get me through today.
I did not monitor sleep, but I didn't turn off the Band overnight either.
So far I am quite impressed with battery life.