Usage time since last full charge no longer showing
After jailbreaking my 3G, I noticed that my Usage and Standby no longer shows up. I've completely drained my battery and let it charge overnight twice now and it still says "Usage times will be shown after iPhone is fully charged."
This will happen every time you restart the springboard. i.e do anything that requires a respring (setting winterboard themes, etc). Fully charge your phone, try not doing any of that, and then check.