Yeah it does, but it's not as useful as you'd think. On my phone, the breakdown is always like 40% Display, 30% Idle, 20% for various system things, and the last 10% is stuff I can actually control. My display is set to auto brightness, but it has a short shutoff timer and I shut it off manually most of the time when I stop looking at it. I've tried low brightness settings but that didn't make much difference. Wireless, Bluetooth, and GPS don't make much difference either but I always keep them off.
The one thing that seems to make a huge difference is having the cell signal on when there is no tower in range. The phone gets hot and burns battery juice when it's trying to find a tower. My office has lousy reception, so on days when the signal is bad my battery is nearly dead by the time I'm ready to go home.
It used to be completely dead almost every day unless I recharged during the day, but I bought an extended battery. They should just come with the bigger batteries, even if the phones cost a bit more. It only sticks out a bit, and makes the battery life much more livable.