Time Zone Off
I live in Reno (Pacific Time) and recently took my 32GB 3G on a trip to Minnesota. I was pleased to see the time change to Central, but since coming home it's stayed stuck there.
The Time Zone is set correctly (never changed it). I have forced some apps to "use current location" but to no avail. I gave up on the auto-setting, but can't find a way to manually set the time either.
Perhaps related, I activated the 3G for this trip for the first time.
Go to Settings | General | Date & Time. Then set your time zone or set the time manually.