Honestly, I think you should just get an iMac! For the money you could easily get a 21.5" and even a 13" air.
Your primary concern with the Air is probably storage space. The weight wasn't a concern of mine either (since I was originally going to buy a 15" MBP), but after owning one a few days you'll get
really used to having a <3lb laptop if you do that.
No doubt, the air should be enough for most people. I've been ok playing games around the complexity of Portal on it as well, although the fan eventually goes to full blast. Then again, I'd expect the same out of a MBP. Having an SSD to begin with helps a TON with perceived speed.
If you want a 17" MBP do it for the 1920x1200 screen, the quad I7, and the tons of space. Even then, 95% of the time the machine will perform no better than an Air unless you're always doing video editing (and most people do not

)
It sounds like you're already sold on a 17" Pro though, so get that! When I bought my 15" PowerBook G4 I
really wanted a 17" and couldn't get one (I needed a laptop before then and the store didn't have any in stock - long story). The last laptop I had before my air was a 16" Vaio and the screen resolution is truly
glorious when you have a 1920x1080 screen (or 1920x1200 in the case of the MBP). I really missed that screen. Oh man.
Really, that screen was awesome! Too bad the rest of the laptop sucked; I was lucky to get 2 hours of battery out of it and the power brick was enormous! It only weighed 6.9lbs, but with the brick I was always carrying 9lbs of laptop around with me when I needed it :'(