Apple has posted an FAQ about the benefits and limitations of their Fusion Drives:
Can I add a Windows partition?
You can create one additional partition on the hard disk with Fusion Drive. You can create either a Mac OS X partition or a Windows partition.
If creating a Windows partition, use Boot Camp Assistant to create it, not Disk Utility. From the Go menu, chooseUtilities. Then, double-click Boot Camp Assistant and follow the onscreen instructions. For more information on Boot Camp see the Boot Camp support page.
There are a lot of other useful tidbits there too, such as how to mount the drive in Target Disk Mode (spoiler: use OS 10.8.2+), as well as some troubleshooting tips. Fusion Drives are shipping now in new Mac Minis, but you can always create your own.
(via CNET, thanks Christopher!)