Andy_Langton - 10:31 pm on Mar 12, 2013 (gmt 0)
Come to that: It's not a bad idea to attach the no-index tag to all your error documents
I'd be careful with this. Google already indexes URLs that are excluded by x-robots-tag headers and robots.txt - that's why they appear in search results (because third party references to a URL are enough to get a URL indexed). You run the risk of creating URLs for evaluation should a search engine prioritise robots directives over HTTP status codes.