I specced my latest desktop specifically to secondary boot hackintoshed MAC OS/X. As the OP says, Gigabyte mobo seemed to be a popular choice. I was looking for an i7 950, so went for a X58A-UD5. I don’t use OS/X much, only for running Ableton really. I can do everything else just fine with Fedora.
From what i read, the main thing to watch out for is the graphics card. The iMac’s mostly use Intel chipsets, which you’ll have no problem finding mobo’s with. But they only used a limited set of graphics cards, so if you can pick a slightly older card with one of the fully supported chipsets. Luckily i intended using an ATI 4870 which was used in a lot of Apple products.
In the end, getting it running was reasonably straightforward. I needed to add a couple of kernel flags to get the graphics card working for the installer. Now it’s fine.
Once i got that working i hackintoshed an old Thinkpad t60p i had lying around.
A tip, if you have a spare drive of the same capacity, lying around. Once you get OS/X installed, “dd” the contents of the working drive to the spare. Until you know how to boot off the media & into rescue mode, if you start playing around with kexts, it’s quite easy to have a non-booting system. (Another tip, once it’s working, leave well alone, you don’t need to touch it 😉
I actually don’t have an issue with the cost of the Apple hardware. I was considering a Mac Pro & compared the middle of the range to a home built equivalent system with dual Westmere-ex, Super Micro mobo, full speed memory, ultra-quiet fans & PSU. That was getting close to the cost of the Apple product & the result would have looked just like any other PC. In the end i opted for the i7 as it provided enough of the Nehalem virtualisation features i needed & enough horsepower.
Edit: +1 having internet access when you do this.