I wonder if there's a small bay in there for 2.5inch drives or something? Be interesting to see the tear downs to find out.
A tear-down will be great. I'm curious to see how easy it will be to add our own SSD drive, or even just a 2nd HD. Apple's two-drive option is pretty damn expensive, but I do like that it will support two drives now.
My guess is that there is room for a 2.5" disk there and ALSO the assumption that such a disk will produce virtually no heat.
In other words, feel free to put an SSD in there aftermarket (I can't see any issues with putting an aftermarket SSD in there), but putting a "normal" laptop drive (say, another 1TB drive) would disappoint both because it's going to "want" to be the default boot drive (rather than the 1-2TB 3.5" drive with much better throughput than any 2.5" physical disk drive) and because it will generate heat.
I'd never put anything besides an SSD in there because it would ruin the thermal envelope. It's a tight envelope inside that slender case.
The SSD + hard drive option is tempting, but Id only want an Intel X-25 80GB in there for OS and apps, and keep my home folder on the HDD. Too bad Apples only option is a $600 256GB SSD. I wonder if the 2.5 bay will be user-accessible after the fact. I dont like the idea of opening up and operating on an iMac (dust, screen, etc.), but to save $600? I might be convinced.
It's actually rather easy to open up. Yes, you want a room free of lint / pet dander / etc, and a good microfiber cloth to clean the glass cover and the LCD screen off before re-mating them. However, aside from the need to use suction cups (I actually used two small hand toilet plungers for this ... it's a very small amount of suction needed), and then to make sure you are carefully following instructions in removing cables (don't just unscrew and lift that big screen out; it's attached with 3-4 other cables you'll need todetach from the "top" down) it's definitely something an "advanced" amateur could do. I mean, I'm a good ten years out from assembling my last PC, and never really had the patience for that in the first place, and opening up the iMac was a walk in the park for me.
Of course, the problem with the iMac HD in the 2009 models is that the drive has special firmware and so can't be replaced by anything but an Apple-supplied drive unless you want to have the middle HD fan going full-bore all the time (see notes on thermal envelope, above). The Apple firmware on the drive puts the thermal sensor output onto two of the drive's auxiliary pins rather than relying on an external thermal sensor, so any other drive in there won't be able to tell the iMac what its temperature is.
I wouldn't expect a similar issue for the SSD, though, as the thermal contribution from an SSD is negligible at best. So, I suspect you'd be able to replace that drive fairly quickly and easily (and cheaply).