@JesterMagic Yes, I mark them as fixed. But they come back and back again. G* used all ever seen links and submitted sitemaps to crawl the site. Unfortunatelly there seems no time limit for old 404s and 410s. I think it has something to do with site history.
@menntarra I think, like all these days you can not infer from your site to other sites. I think sites with "penguin/panda" flag have other criteria for quality ranking.
Googlebot couldn't crawl this URL because it points to a non-existent page. Generally, 404s don't harm your site's performance in search, but you can use them to help improve the user experience.
Read between the lines!
Panda Update today? We have -50% and lots of new silly affiliate/spammy pages in index. Must be a quality algorithm update.