Interesting thread... This guy there with "a source" is claiming the new iMacs will be:
26", refined to 25.5" LED backlit display, 21.5" display on lowest model
All with Clarksfield
Up to 12Gb RAM, new CPU, likely to be Apple-first
Minor shape changes
Up to 2Tb HDD
New mouse design, backlit keyboard
9th October release
20" replaced with 21.5"
[and I forgot]:
3xUSB 3.0
Also, not specifically iMac-related:
Blu-Ray available for EVERY Mac, requiring 10.6.2.
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If this is true, that would be great. We shall see!