Apple released iOS 4.0.1 to better represent the reception issues. According to Apple’s PR iPhone’s Reception Bar Formula is wrong, thus they are showing more bars of reception than it actually have! With the new update from iOS 4.0.1, you will realize that your reception at home or in office will be much lesser than you had previously(this is what I felt).
Look at the Reception bars, it is really slightly bigger and longer compare to the previous version. I don’t think it helps at all for showing bigger bars, but maybe it is a mental thingy that I don’t understand. But one thing that I realized after the update is that my iPhone 3G felt faster and less laggy after the update! This I can’t confirm yet as I have just updated my iPhone 3G only 2 hours ago, but definitely feel faster!
I will post a update if I can confirm that this update actually makes iPhone 3G running iOS 4 faster.