I noticed a few of my sites had a nice week over week boost from both Bing and Yahoo early this week. Two other sites I manager saw ~15% drop in traffic from Bing and Yahoo. The sites are unrelated, and hosted on different stacks, so I don't think it's a technical issue on our end.
I checked [serps.com...] and they showed a big spike in Bing volatility on May 7th 2014. I also checked [serpmetrics.com...] and they showed +100% in Bing flux on May 5th.