I'm planning on purchasing an iMac and I'll mainly watch movies and play Warcraft III once in a while, so what is more essential, everything else being the same: 17 inch w/ 2GB RAM, or 20 inch w/ 1GB RAM?
Definitely the 20''. Can't upgrade the screen later, but you can upgrade the RAM.
Besides, at 1GB of ram, you don't even need more ram. You can get more for better performance, definitely, but once you pass 512MB and into 1GB, you'll see satisfactory performance. And yes, it will run WCIII well.
I totally agree with everything said here. I purchased my first Mac yesterday, a 20" iMac. Although I do eventually want to upgrade it to 2GB, it is already very snappy on 1GB, even with some Rosetta apps running (like Office 2004), and as it has been said -- you can always upgrade the RAM but you can't upgrade the screen. I bought it in the store so I stuck with the 128MB of vRAM, especially after reading benchmarks that indicated at most you got a 3-5% increase in gaming performance by going for the 256MB of vRAM. Besides, I don't game all that much. But I did setup XP on BootCamp tonight, and played UT2004 at full 1680x1050 resolution with Normal to High graphics settings and it was smooth as butter. Granted, that game isn't one of the latest and greatest, but that's what I benchmark things with. I'm going to try FEAR multiplayer next.