As suggested by a certain commentator in my last post, I started using JuiceDefender. From the first day of using it, I was a little impressed by its performance. Now, although yesterday was "normal" or slightly towards the "light" side of the spectrum in terms of using the phone, the over-a-day battery life is still very good. I'm not saying that this is all JuiceDefender, but definitely give it try.
In addition, here is the screenshot of yesterday's usage. At one point, it actually bounced back a little bit. Hmm...interesting.