Webmasters are reporting over at WebmasterWorld that MSN Search has been dropping pages of their sites. I am not sure how similar these reports at to the Google issue but it seems that it is about "site quality" as well.
The thread creator said;
Can anyone tell me if they experienced this lately on MSN Search. I had a site doing quite well for some very good keywords, top 10 rankings. Site has about 12 pages internally and about 20,300 backlinks according to Yahoo. As of a week or two ago when I do a search for MYdomain.com I get a total of 4 pages back and they do not include the index.html page. I wrote to MSN Search and they gave me a reply stating that only high quality sites will rank well and maybe my site is not linked correctly (the index page is linked to from every page on the site)?
Now he is completely out of the MSN Search index. Many other Webmasters have reported similar results from MSN Search. Some believe it may have to do with MSN not handling 301 redirects properly, but not all are reporting 301s as the issue.
Forum discussion at WebmasterWorld.