I had a graphic designer working with me and used his own MBP in 2010, he claims that he bought his MBP for 3 years [2007 i guess].
He used the MBP for photoshop, wireless during working hour, and his MBP really last him for 6-7 hours.
But after I got my MBP and reading many comment from my MBP friend and over the internet, seems like we are squeezing the MBP to just get a little improvement. I guess 7 hours is an historical index and not applicable into new MBP. just that Apple never update this historical data.