How long should my MacBook Pro battery last?
It's likely that you are running something in the background (such as Skype) which is triggering your dedicated graphics card, despite it not actually doing anything graphically intensive. This is a known issue in Apple's graphics card switching technology.

Download and run gfxCardStatus and see if I'm right. If so, close the problematic program or use gfxCardStatus to manually switch to the much lower-powered integrated chip. You should get longer battery life after that; I haven't directly measured it but I know I get at least 30 minutes to an hour of extra life.

And of course it also depends on what you're doing with your computer, what background programs are running, the brightness of your screen, etc.