I found this thread after search for the topic.
I too had all the site on one VPS fall out of indexing on Bing, this happened at the same time as others have said on here mid November.
Since about then I've had to battle Bing support to try and get answers. The first 5 or 6 replies kept saying the site wasn't blocked, this was simply because the support staff just didn't know how to search the Bing index.
Once I had proven the site were in Bing and then had fallen off it was sent to the back support to investigate. But there yet again, although I had emails telling me they were looking into it and I should expect a response in 84 / 24 hours I still had to chase it up after waiting another 3 weeks.
The response I got "Upon further review, we have identified that a block is in place against your site as we are seeing that your domain, http://www.example.com/ is associated with bunch of irrelevant/spammy sites."
I would suggest this is a bit less then the sort of professional reply I had hoped for. Apart from never resorting to spam my site is very relevant but even if it wasn't what is that got to do with Bing.
They way they talk about other sites its as if my site has been punished for either linking to them or from them. But I don't know which they are talking about. My site does not have what you might call "risky" links on it and I can't stop other linking to it. About the worst any of the sites on the server has is affilaite links - no one ever got hung for that.
The reply goes on to suggest I make changes to the SEO of the site. Fact is the whole site was redesigned after Bing banned it, it's all totally new data and SEO. Did they recheck ? or have they just sent the response to cover their backs for doing nothing all this time ?
This is a site that is ranked 3 in Google and before bing combined the site had 70,000 pages in yahoo. So I've lost a lot of traffic and a lot of money.
I suspect they have put in a subnet ban to stop spammers and my VPS had the misfortune to be moved to that same subnet in November as all the sites on the VPS have fallen off Bing at the same rate and the same time.
I've asked for clarity as I don't participate in the black arts of Seo. I have customers who wouldn't know where to start on that subject but the only action I can take to try and resolve this is move hosts. That means 20+ site, 8 customers.
[edited by: tedster at 2:12 am (utc) on Jan 17, 2012]
[edit reason] change domain name to example.com [/edit]