One of my site for the last two weeks lost 48% in traffic from Bing (higher from Yahoo). Still trying to figure out what keywords were affected. This is a Technorati top 100 blog, and the traffic drop is pretty sizeable. Not affected by Google Panda, though.
Our site experienced rankings drop in Bing & Yahoo lately for the key head terms in our vertical. I saw our ranking drop from position #1 and #2 to around #8 and #9 for key head terms in Bing & Yahoo, but the same keywords rankings in Google remained stable at #1 or #2.