On the same day as Panda 2.0 was rolled out on Google (around Apr 11), my site (affected by Panda) also dropped out of Bing and Yahoo. Referrals went from around 1-2000 per day to nothing.
I think it is a coincidence, but I'm unsure what to do next. I sent an email to Bing support and received this response "we do not see any discrepancy for your site on our end so there's nothing that we can work on to have this resolved."
They suggested going to the Bing community forums, but frankly these are overrun with spam, and I see little point in posting there.
When I do a site: query in Bing, they show "1-3 of 4,730 results". And then proceed to list only the home page and 2 other pages... Everything else is missing.