[How-To]Getting Better Battery Life
This is what I've done to help my battery life.
Firstly you'll have to root your device, then follow the steps below.
1. Install SetCPU(from Market or where ever you can find it)
2. Run it, allowing root access when asked by superuser.
3. On the Main tab, set Max and Min to 1200000(1.2Ghz), or whatever you want general usage to be. Most users probably want it like this so it will stay at best performance during using, and will not slow down. Also, whatever speed you're using set Scaling to Performance. Even if you are not running at top speed, it is still good to use Performance for the settings you want while using the device.
4. Go to Profiles tab. and check Enable, and click Add Profile. Set it to Screen Off, and you can change the settings to whatever you want. I had it at 100000(.1Ghz) for Min and Max, but when you go to unlock your screen, it lags a lot for a second. I currently have Max and Min set to 400000(.4GHz), and it made it so it does not lag when I go to unlock, but it is still low enough to be very conservative on battery. Set Scaling to Powersave, and Priority does not matter unless you have more than one profile, so don't worry about it.
5. (Optional) Install JuicePlotter from the Market, for free, and it has a nice widget that collects your phone data and after a few days will become very accurate on phone battery life remaining. It will show it after a day or so, but it will tell you how accurate it is, and it might not be very high until a few days later.
And that's it. Whenever your screen is off, it will underclock the processor so it's not using as much battery when not necessary. If you want, you can add other profiles, such as for when charging, and when the battery is low. I originally had it set to 1.2 GHz Max and Min while charging, and set the priority higher than the Screen Off, so it didn't clock down if I turned the screen off while charging, but there is no reason, I'm still not using it when I turn off the screen, so I deleted that profile.
So if your only profile is the Screen Off, then once you turn the screen on, it will change to whatever settings you have on the Main tab.
I unplugged my phone at 6:30 AM, and it is now 5:30 PM here, and I still have 32% battery, with JuicePlotter telling me I have 4 hours and 49 min left, but it only has a 72% accuracy since I just got the app yesterday. That's great since yesterday my phone would have been dead over 2 hours ago. When I woke up JuicePlotter said I had around 15 hours, but it wasn't as accurate as it is now, and it so far is expected to last longer than that..