You know what?
After reading all the threads about screen display quality and such I have come to the following conclusion.
NEVER make an opinion about a screen display using solely information provided by others. Use YOUR eyes, go look at what you are considering purchasing. Make your decision based on your own observations.
Some will tell you the 20" is great. ( they probably own 20" units )
Some will tell you the 20" bad. ( they probably own 24" units )
Go out and test drive a 20" iMac, look at it from all angles you might expect to use it from. If you are gonna use it standing on your head, with your feet hanging out the window ... test it like that.
Don't " refuse to buy it " because someone says .... " the ____ sized screen looked bad when standing on my head with my feet hanging out the window " if that is not how you plan on using it.
Personally I own a 24" iMac. When I went to buy it I looked at the 20" units though I knew I wouldn't buy one. My reason for not buying? I just sold a Power Mac and 22" LCD display, I did not want a smaller screen so the 24" was for me.