Here are my battery calculations. And yes, I feel like a total nerd for figuring this all out like this.
Normal:
50% screen brightness
Auto-Brightness = ON
Bluetooth = OFF
Wi-Fi = ON
Three Mail accounts, fetching every 5 mins.
Activities: Mail, iPod, Safari, occasional games, Notes, Youtube, and Videos.
Battery Life: ~12 hours.
iBooks:
Same settings as above, but wi-fi OFF, and obviously, just iBooks running.
Battery Life: 14-16 hours.
Minimalist:
10% screen brightness
Auto-Brightness = ON
Bluetooth = OFF
Wi-Fi = OFF
Location Services = OFF
Activities: iPod, Notes, Videos, and other non-wi-fi apps.
Battery Life: 18-20 hours.
Now, I've tested all of these on my 32GB wi-fi iPad, and these are the numbers I've gotten. Most of the time, I keep it on the normal settings, and end up charging every third day.
At night, I'll use the iBooks setting, and read for hours. The boost is significant, but could be to the lack of other processes. iBooks obviously doesn't take much to run. While the screen brightness is diminished from it being darker, this is countered by the screen remaining on constantly, where with usage of some other apps may find "down time" in between activity (specifically iPod, Notes, and similar apps that may be left alone for a few minutes, allowing the screen to turn off.)
The minimalist setting is limited - obviously, because there's no wi-fi, and the screen just isn't as pretty when it's brightness is so low. There's still visibility, but obviously it's much nicer to watch movies or take notes with higher brightness settings. I could see this being useful for someone who is out and about and needs to be taking notes, or isn't on wi-fi and needs some lasting battery life. That being said, despite the huge gain in battery life, in my opinion it's not really worth it unless it's a necessity, as you're limiting yourself quite a bit.