Apple wasn't kidding when they said they made the thinnest, lightest 17-inch notebook on the market. The 17" not only weighs slightly less than my current 1-year old 15" Asus notebook, but is only an inch wider. The 17" is only 15.5" x 10.5" x .98", compared to my friend's 17" Dell which is 16" x 11.5" x 1.7"(almost twice as thick as the MBP!), not to mention it weighs more than EIGHT pounds.
You won't regret it. I was really close to getting the 15" because I was intimidated by the seemingly massive screen on the 17", only to realize that when it comes to desk space the 17" doesn't take up that much more than the 15", and is just as portable.