I have used several kinds of 1X to 16X risers.
This one in particular, is by far the worst:
http://www.ebay.com/itm/261433040898?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITI'm in the process of replacing them all. The major fault of this riser is having a card go offline (as in not showing up on aticonfig --list-adapters). If a card goes offline, the miner goes offline usually. Replacing this riser has always cured this fault. This particular riser is also mixed in with other types which makes fault isolation easier.
I've had trouble with a few other risers, but explaining to the relevant ebay seller the technical issues is hopeless. Most of these guys sell hundreds of items and any kind of return is hopeless and not worth the hassle.
I believe the problem with this particular riser is the ribbon cable mechanical attachment at both ends. I believe this particular pressed mechanical attachment results in an uneven contact area. If the contact area is small your jamming more current through a smaller pipe. My stuff gets pretty warm at midday, so it's also possible that the mechanical connection is oxidizing. The small gauge of the ribbon cable conductors just enhances this problem.
The solution I use is to use risers which are either soldered at both ends or USB based risers. With USB risers you are leveraging a standard that for years has transported high frequencies as well as DC currents.
FYI - All risers have their own power connection direct to the power supply.
