The new iMacs have the super fast Thunderbolt port and Intel's latest Sandy Bridge Core processors which makes them, well, pretty awesome. What's not awesome? Apple has made upgrading the hard drive on the new iMacs damn near impossible.
Other World Computing is reporting that "the Apple-branded main hard drive cannot be moved, removed or replaced." They say it's because Apple has altered the SATA power connector from a standard 4-pin configuration to a 7-pin configuration. And since hard drive temperature control is regulated with this cable and Apple's proprietary firmware, messing with that drive messes with everything. OWC says:
From our testing, we've found that removing this drive from the system, or even from that bay itself, causes the machine's hard drive fans to spin at maximum speed and replacing the drive with any non-Apple original drive will result in the iMac failing the Apple Hardware Test.
They tried every workaround they could think of but couldn't use a hard drive that wasn't ordained by Apple. In short, it looks like if you want to upgrade your hard drive, your only option is to go through Apple (or alternatively, use the second drive bay). Not cool. Read the full report at OWC.
Update: Possible logic for this move: iMacs aren't meant to be user serviceable, so Apple's looking to economize the design by reducing the number of parts—removing the separate external sensor/cable monitoring the HDD's temp in favor of an integrated sensor. (Mildly analogous: Soldering flash storage chips directly onto the logic board of the MacBook Airs. Less complexity, but the trade-off is it's not user replaceable. SOP for Apple, really.)