I'm showing that miners on Ghash.io are having the same problems. But Slushes so far are showing the worst out of anyone I checked with.

It may be the hubs where a lot of the traffic goes out or comes in to the USA. All it takes is one of those massive units to blow and
it can effect a lot of Internet activity. (Then again, maybe slush is pulling the plug out and saying....just kidding! Then plugging it back in!)