Stock without any mod or any program like Juice Defender running and I'm getting easily 1 full day on a full charge and with Wifi on the whole day. I'm not on 3G but I receive Yahoo, Gmail and Ebay updates constantly throughout the day with Wifi if that helps.
Did you tweak the screen brightness? I unchecked on the phone's auto brightness and set it on my own. The bar is way down as I don't need bright indoors. I think if using it outdoors under sun, the screen needs to be broghter of course.
Well to put it the other way around, the reason you don't see any difference when suing screen protector is because the LCD screen is damn excellent already.
I believe it will only scan for Wi-Fi
continuously if you are on the "Wireless & Network" > "Wi-Fi Settings" page. At other times, it will only scan periodically. No idea on the interval because when I'm at the airport or places when I know there is Wi-Fi, I don't get the notification instantly. I will only get it 10 minutes later or when I access my phone. Of course if I go to the "Wireless & Network" > "Wi-Fi Settings" page, I will surely get to detect the Wi-Fi AP instantly.
Strange. Earlier on December 8th, I got an automated SMS from 62003 saying that my phone's warranty is from
05/12/2011 to 04/12/2013.
For the fun of it, I just sent an SMS to check and it turns out that the warranty is from
09/12/2011 to 04/12/2013. Hmmm... A few days also want to short change me meh?
Got... Akan datang.

Next question... How much did you pay for it?
What Wi-Fi router are you using? If there are a lot of Wi-Fi signals and other 2.4GHz signals in your neighbourhood on the same channel as you are using, then chances are the signal will be very crappy.
Off topic... How do you access the house address with IC number?

my screen brightness is set on the lowest manual.
i'm using the free version to turn off 3g when screen off.
free version cannot control wifi.