Dont Hurt Me said:
Beware of any machine pushing GMA950 or any integrated graphics, they sucked when Apple wasnt using them and they suck now. They are $4 graphics that companys can make big money on by screwing the consumer. If you are buying a new machine find a PC or Mac that has a real GPU in it. You will get years more life out of it. Thats my 2 cents. Now get ready to hear from all the Low Power I love crap butt graphics people who want others to have crap butt graphics. Future proof your machine with a decent gpu.
I'm so sick of your integrated graphics bashing. Honestly, if someone isn't doing 3d or extensive gaming, then they're not going to notice the difference between the GMA950 and a dedicated card. What YOU use YOUR computers for is one thing.. but keep in mind that most consumers are not in the same boat as you.
For occasional gaming, the GMA950 can do just fine if you have the extra RAM. I've run games on mine and they work just fine. For extensive gaming or the newest titles, even the iMac's GPU isn't sufficient at the highest settings, so I wouldn't really consider that in your decision, IMO. I mean, hell, even the stock Mac Pro isn't a good gaming rig.
Here is a good thread to look over with game results on the MB.
As far as school and portability goes.. I find it VERY helpful to be able to take my computer to and from class. Notes, quick access to assignments (no more "oh crap! I left it in my printer!" problems), internet.. Most of my teachers talk too fast to keep up with using a pen and paper.. if I weren't typing it all up, I would miss half the lecture. However,
thedude110 brings up good points as well - I think, ultimately, it's up to you to decide which approach will be best for you.
As a general rule, though, I think it's safe to say that if you don't absolutely
need portability, then go for a desktop. Usually you have faster processors, more space, more RAM possibilities.. BUT these advantages are somewhat cut down on the iMac, since it's not really a full-fledged desktop in the conventional sense (not as many RAM slots, mobile processors, HD bays, etc). I still would probably consider the iMac a better bang for your buck, though, so the rule still applies.