aristotle - 10:14 pm on Dec 10, 2010 (gmt 0)
What about when people try to link to your site, but mis-spell the file name or use .htm instead of .html.
For one of my sites, Google Webmaster Tools shows more than 20 of these non-working backlinks in the Crawl Errors section. Most of them are from forums where somebody tried to link to one of my pages in a forum post, but mis-spelled the file name or used the extension .htm instead of .html
I wonder if Google uses these non-working backlinks in some way as a kind of citation.