My iPod touch started NOT holding a charge the same day I did the OS4 update. It has been downhill from there. I'll post everything I've tried in attempts to help someone else and also to get help narrowing down the issue. I'm a software tester myself, so I've tried a few things:
1. I did a restore as new device (not backup) in case there was a bug in one of the apps. I did the restore and immediately dragged my apps back onto my touch. That night, the same thing happened. (lost notes and calendar in the process

)
2. I did a restore as a new device and left it alone over night. Didn't touch the iPod after restoring it. Held a charge fine over night...
3. Added one app (Tap Ranch) to the iPod. Died overnight...
4. Did another restore from new device and added a different app (TextFree). Died over night...
5. Did another restore from new device and added a non-WiFi app (Hoggy) per Apple Technical Support's request. Worked fine...
6. Did another restore from new device and turned on WiFi for the night... worked fine...
7. Apple finally decided it was a hardware issue. They gave me a new device yesterday. Same thing happened over night though.... SUPER mad since I lost ALLLLL my game data...
One time I was in the mountains, out of WiFi range and it worked fine for 3 days and I never turned WiFi off. I'm narrowing down that the issue has to somehow be related to WiFi, but it only started occurring after the OS 4 update. I was told the 4.1 update would fix it, but it didn't. The issue is obviously in the new software. Not sure if it is in the multitasking or what. A complete power off will not discharge the battery.
Turned location services off for tonight and will try it that way. If not, tomorrow I will try turning WiFi off over night and try that.
Sorry so long, but I wanted to put all the info in here.
Hope this helps and any further info is greatly appreciated.