Not sure, but that is a GREAT idea! Not sure it would be possible though. Phone use is so sporadic. How would it determine what's left? Talk time, music, web surfing, etc. I could be wrong, but it seems that there are too many variables for this app to predict effectively.
5 1/2 hours of usage, about half of that on the phone while tinkering, about 1 hour of tinkering off the phone (using GPS, 3G, and a few other programs), screen is set low for brightness but it's still quite bright to me (about 1/4 setting). It's at around 65% battery life. (+/- 1-2%)
I Totally agree with that article, people need to stop thinking of this as a phone, its not, its a full blown computer. Try taking your laptop out and keeping it running all day and see how long it lasts.
Some other things they didn't mention in that article, you need to turn off the WiFi and Bluetooth if you dont plan to use them for a while, they will activly search for connections if they dont have one and that eats power.
Personally I bought 3 media stations and a car mount and charger, If I'm at my desk at work or home, I put it in the media bay infront of the screen, makes a nice clock too , if I'm driving, I put it in the car mount and plug it in, and I decided to use it as my alarm clock too, so I have a media station beside my bed and it gets to charge all night.