I'm using the adapter with good results. Not to say the negative issues pointed to aren't valid. I would consider just running a couple of wires beeing just as good, if not better than the adapter, as it keeps one big connector out of the loop.
One advice along the road tho, to avoid grief: run your CPU, board and boot devices (any disk/optical you wanna boot from) off the primary PSU, as the second PSU will have a split second delay in powering up and may spin up the drives a little to late for the BIOS to detect them. I run the gfx and most of the fans (only one of the cpu fans run of the mobo, the rest from the second PSU via fan-adapters)
Pressing the reset switch after initial powering up will ofcourse fix the delay in surge from the second psu, and you will have a clean regular boot