27" iMac non-native resolutions

So, I'm doing what a lot of folks here are doing right now, (im)patiently waiting for my new quad core 27" iMac to ship. In the meantime, I've been doing some thinking. I intend to game quite a bit on this new system, and I'm concerned about the resolution of the screen. Obviously, even with the HD4850, most games are not going to tolerate the massive resolution required of this huge screen. So obviously, to maintain decent frame rates, I'm going to have to lower the resolution. Now, I don't know much about LCD technology, but what I've heard is that how good the image quality is at non-native resolutions is dependent on the hardware in the LCD panel. From what I've heard, this is an excellent display, with all the latest bells and whistles.

So, my question, for anybody that has experience with this particular screen, or another like it, how does it handle non-native resolutions? Does it look good? Abysmal? Somewhere in between? And, if I'm going to play in a non-native resolution, I suppose my best choices would be 1920x1080 (3/4 res), or 1280x720 (1/2 res). Am I correct in that assumption?

Thanks so much for taking the time to read this, and I hope this makes for some good discussion!