Video Card and RAM
The iMacs, more than anything (well, the mini's too) are in a desparate need of an upgrade. The iMacs are desktops that use laptop components, so they take an enormous hit right there.
First, the graphics card x1600 is 2 years old, and a laptop graphics card. it's fine for a laptop, even though so many people are demanding new mac book pros. but the iMac is a 'desktop', and in that line the card is way, way overdue for a change.
Second, the RAM. How can you buy a desktop the maxes out at 3 gb of RAM (well, for all pratical purposes, it's really 2 gb)? Any new computer desktop sold should come with a bare minimum (not near maximum) of 2 gb with upgrade ability to at least 4 gb, but hopefully 8.
Well, with the new Santa Rosa platform (a laptop setup that i am sure will be used in the desktop iMac) and the release of new Nvidia mobile graphics cards, hopefully this will be addressed.
Of course you could always shell out $2.5k for a mac pro!! (which is reasonable if you need a workstation, but seriously, let's update the other stuff)