I tried yesterday to perform a request to have some content excluded from search engines, and noticed that __NOINDEX__ does not work on the main Meta-Wiki namespace.
Given the nature of Meta-Wiki, the NS_MAIN works differently as it happens on the rest of content projects. We don't store encyclopedic content ther. All cross-wiki stuff, such as vandalism reports, RFCs, etc. does get indexed and sometimes search engines do show those "negative" remarks as first results. This does not only happen to NS_MAIN but on many other namespaces. We've got several requests in the past to hide from search engines some pages and we've found that the only way to do it is by modifying the robots.txt, which requires an admin.
On some other projects those pages do get NOINDEXed via adding the magic word or by modifying the robots.txt file, or both. Meta-Wiki should operate a different policy and allow the magic word __NOINDEX__ work on all namespaces, included NS_MAIN.
I wonder if we should set them to nofollow as well.