I looked for lots of information about Target Display Mode and the information just isn't that good. I'm pleased to say that it works better than I'd expected. I took a PC with a DisplayPort output, got a displayport to mini-displayport output and plugged it in. Upon booting it is instantly recognized by the imac and it switches over to Target Display mode where it worked as expected. As a bonus, I couldn't find confirmation that the iMac will also use audio - it does. The GTX970 in the PC (and most video cards recently) can put audio through the displayport. So, I have audio, video it works perfect. Hit CMD-F2 on the iMac keyboard and it switches back to Mac. The audio and brightness keys on the Mac keyboard still work. It's a perfect solution EXCEPT I think the external (Firewire and USB) drives disconnect from the iMac when it is in target display mode. Has anyone seen this behavior?