Hi
I'm considering upgrading to a 24in iMac - the extra screen space would be useful. However, I see that there are some good deals on the outgoing 'white' iMac.
The biggest difference in the old and new Mac is the screen. Apple went cheap on the new screens but every other part is better
How to decide is to think about how you will use the new Mac. Do you do serious photography and video editing were you care about things like color fidelity and monitor calibration or do you mostly surf the web, watch DVD movies and play games? The new screen is well suited to the later but not as good for critical creative work.
I think the new glossy screen is like lite beer. Some very smart marketing guy found a way to sell cheeper beer with extra water added at the same price as "real" beer. Using "lite" was smart because people would not buy the more actuatly labled "watered down" beer. With LCD screens "glossy" was the smart marketing term because the more actuate "reflective" or "sans anti glare coating" just would not sell.