Besides the obvious screen size and the video card are there any other differences in the 20 and 24 inch iMacs?? A friend of mine wants to buy an iMac (after Macworld) but is having a hard time deciding between the two. $500 seems like a lot for 4 inches of screen and a different video card. She is going to be using the Mac for Photoshop, Aperture and some light video work using Final Cut Express. Is the 24 worth the extra $$ for her?? Any suggestions?