The problem with Apple's laptop and all-in-one systems: they've never exactly been easy to upgrade. Even an every day task such as simply replacing the hard drive can be an incredible chore. When Apple released the unibody Macbooks, this task was made a lot simpler by having it locked under a simple panel with a latch. The folks at Ifixit have disassembled the new iMac already, showing it's guts to be quite a mess. The iMac pretty much requires you to gut the whole system, including removing the screen, just to get at the hard drive. This is in contrast to the original G4 all-in-ones where you simply just had to remove the back panel.

The disassembly also had some other things worth noting. First off, the CPU appears to be socketed rather than soldered. That means it should be upgradable with any Penryn based 35W or 45w TDP, Socket P based processor. Presumably the iMac uses the C2D T9550 (2.66ghz) and T9800 (2.93ghz) and Core 2 Extreme X9100 (3.06ghz). The hard drive is a standard 3.5'' 7200rpm SATA type. In addition, the screen is backlit with CCFLs rather than LEDs like the new Macbook models. I find that odd that they didn't go the LED route since not only do they use less power, they also produce better contrast.

You can check out the whole disassembly process here.