Google have announced a new feature in their Webmaster Tools. In a nutshell it will display all pages that link to a missing page on your site – you have a chance to fix it or take advantage of it.
So, if a site was linking to an erroneously spelt page then you could create a redirect for this to the correct page – ensuring you still get the visitors to the appropriate page.
BMTG was okay (apart from a misspelling on my own blog, so I was able to correct that) as was Copy+. However, I can see the advantage of this tool and will be keeping an eye on it in future.