A lot of this comes down to what you are going to use it for. If the majority of your usage will be email, web, and writing college papers in Word, the 17" is much too much screen space. Remember, the resolution of the 17" is the same as the resolution for the 20" Apple Cinema Display! A lot of it will be wasted, yet you will always have to carry that extra with you. If you are going to college, you will probably be carrying the laptop constantly, so size and weight will count.

The users who get the most out of the 17" are those who work daily in apps with a document surrounded by 20 palettes with 50 little controls and sliders in each palette, so they need as much room to spread out as possible. Final Cut Pro, Photoshop, Aperture, Logic, those kinds of apps. If you are not using those kinds of apps, you should ask yourself it the 1440x900 screen of the 15" is probably enough. For me, it is. I'm always going to have a 15" because I like the modest size.

The other argument in favor of the 17" is spreading out multiple apps. If you really want to have email, web, Word, and chat windows all open simultaneously without overlapping each other, then maybe the 17" is better. But if you enjoy using Expose and Spaces to manage screen space, then the 15" might be enough for that.

Screen space is most of the reason to get the 17", because Apple doesn't do much else with that extra case space. They don't expand the keyboard for you, they don't add another accessory/drive bay, you can't add more RAM than the 15", and they don't add ports or slots except for 1 more USB as far as I know. If Apple took better advantage of the bigger case, the 17" would be more compelling.

I'm wondering how much better the 17" model deals with heat. I'm also wondering if 7200RPM will run too hot.

Mostly audio production and designing.