We tested 22 USB 3.0 memory sticks, USB 3.0 external hard disks and USB 3.0 external SSDs. 14 out of the 22 devices exhibited the problem.
If you want to be sure that you buy a motherboard without that issue, you will have to wait. Intel has indicated that, starting end July, a new version of the chipset, C2, will be supplied to the motherboard manufacturers. Then the motherboards have to be produced and shipped, and retailers will of course first sell their existing stock.
You can't tell by the exterior whether a board is C1 or C2. The manufacturers are also of the opinion that it's insignificant and we haven't heard any plans that it will be mentioned specifically on the box which version it is. Once you've bought a board, you can find out which one you have with CPU-Z. Under the tab Mainboard you can see the revision of the chipset. Revision 4 is C1, and the improved C2 stepping will be called revision 5.
You can read more about this and everything else there is to know about the new chipsets and motherboards for Haswell processors, in our big test of 33 Haswell-compatible motherboards.