Matt Cutts wrote a post about the announcement on Google webmaster blog
, where Google stats that you can tell who is linking to one of your 404′s. This means that you can ask sites to link to another page of your site instead, thus avoiding the loss of links.
Using Google webmaster central you can get a list of 404′s and also a list of sites linking to each page.
For more info read Matt’s blog post.
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