I think the biggest thing you get with AHCI is the ability to hotswap the hard drive. That's much more useful with, say, an eSATA drive or a drive that is not your primary system drive than for your system drive. And I think some optical drives have problems with AHCI mode, but then some motherboards let you set AHCI/IDE mode separately on each SATA connector.

Hm, thanks interesting.

The eSATA drive is controlled by a different controller (the J-something rather than the Intel ICH9 controller) so that shouldn't be impacted. And the optical drive shows up fine so that's OK.

My biggest concern is that of backup/restore stuff. I know that if I installed Windows with the drive set as AHCI I would have had to supply a drive during the install via a floppy disk: there's no floppy disk in my PC :) I have a USB floppy drive but who knows if that'll work. I guess if I had a HDD failure and had to restore it, I could pick up a floppy for exactly that purpose, but even so. If the only thing I get is hotswapping drives that are internal, maybe I'll flip flop back to IDE and not have to worry about it.