I have the same problem, but I can remember when it started. My girlfriend's iPhone doesn't have this problem and I updated both of them at the same time for 1.0.1 & 1.0.2. Mines a 8gb and her's is a 4gb. I have done a restore with no luck.
I don't have that problem, but my usage time is significantly higher than it should be. My guess is, BT while in my paired car is considered usage, even when I'm not on the phone. But, its just a guess to try and explain why my usage is so high. If I'm right, then maybe having a BT headset turned on is being counted as usage?(even not on the phone, just standby)
I can get a full charge, unplug it, and then check my usage. It says 0 for each. But after a few minutes I check the status again and it says the message about how usage will be populated after a full charge.
I wonder if the NullRiver Installer.app is causing problems.