I bought some cables from
http://www.b2c-support.com/pcie-pciexpress-16x-riser-card-extender-ribbon-cable-p-4154.html.
The first two out of the five I tried refused to recognize the card. The third one however, is when it gets really interesting.. I plugged it in, standard procedure. Made sure there was no possibility of shortcircuiting the exposed (why exposed?) contact points.
So I'm all set up and ready to go. I flip the PSU into on, and hit the power button. First I noticed some really thin smoke, it was barely visible. Then the smell of burning plastic and suddenly a lot more smoke. This is what I pulled out:
http://i1081.photobucket.com/albums/j349/drknark/IMG_0517.jpgLuckily all my hardware survived. Since their support ignored me I had to issue a paypal dispute to get my money back. So don't buy cables from that site

I would even be wary of similar looking cables at other sites, might be the same manufacturer.