I put some in a system I had about 18 months ago. It had a soltek board with a AMD 1400+ M.P. 512 sdram and 2x40 gig hard drives. I got mine from a computer fair and I think I paid £10-£15 for the set.
I did check temp's against ordinary ribbon cables but found only a difference of one or to degrees C.
I was asked if I would sell it and was offered £200 more than it cost to build. Bye bye computer.
The thing I liked about them was that they did make the innards of the system extremely tidy.
I have on a couple of occasions split an ordinary ide cable down the spine with a trimming knife. You can get the same result, but they are never as tidy. Plus the success rate ain't good as the slightest deviation and you have a knackered ide cable. lol