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wouldn't you rather just connect your iMac to a big screen tv? then you can use a 42" tv screen with it and also have the flexibility to watch tv, itunes movies, blue-rays etc.....

You could go as high as you could afford with a tv option.
 
At this rate you could probably expect a 30" in the near future as they already provide such monitor as a standalone....
 
Apple's big reason for using the 27 inch was for securing a forfactor to fit in those high tdp lynnfield chips in the high end iMacs. About the only thing Apple could do with a 30 inch iMac would be the probability of fitting in SLI'd/crossfire'd mobility gpus or a desktop gpu. Seeing as how Apple doesn't focus on graphics performance, but rather cpu performance, I see no need for them to up the screen size again (especially since every new gpu/cpu with each release has a smaller manufacturing process and thus less heat produced)
 
I don't think there will be a 30" really.. Since they're launching the 27" standalone screen they seem to go stay with that size. Seems to fit.. Being consistent =) like with the Iphone screen size ;)
 
You guys seems to be talking about now or in a few years. I'm talking about maybe 5 years and up.

I saw a concept of an iMac that is very thin, HUGE screen, no black borders. probably a streamed OS to get the iMac to be so thin.
 
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