There are many factors that impact your battery life. See the BATTERY LIFE FROM A CHARGE section of the following link for details, including tips on how to maximize your battery life.
This should answer most, if not all, of your battery questions:
Typically I have Safari (3-6 tabs), iCal, Mail, iTunes, and Evernote open. Generally lasts 6-7 hours. If I am playing lots of videos from websites that time cuts off about an hour.
I can make it just about all day - using mail, safari, pages, numbers, cal, Skype occasionally. I've got 1:41 left left and have been at it since 7 something - on and off.