This is probably quite variable for everyone, and depends a lot on how you use the machine.
I have managed to get approximately 10 hours of actual use out of the machine which includes majority Safari surfing, emailing, some word processing, etc. Bluetooth is off. My screen is usually 50-70% brightness. No music playing. Incidentally the other night I watched a 2-hour movie and it didn't appear to drain the battery much.
Tonight I've been using the system for around 5-6 hours so far, including being on FaceTime for 20 minutes and listening to a 80 minute audio file. The battery still indicates 46%. The other night I found that Google Video chat uses a quite a bit more power.
The Significant Energy monitor is pretty good for me at estimating apps that use a lot of power. If I started a power hungry app, like Civ 5, the entire thing can drain in 2 hours or less.
