Matt Cutts on Preventing Virtual Blight

What is virtual blight and how do webmasters prevent it from happening?

If you missed the Web 2.0 summit, like I did, then you can checkout the YouTube video and Google Docs slides that Matt Cutts has done very nicely for us, a second time around,

See
Google Docs: Preventing Blight by Matt Cutts.
Official Google Webmaster Central Blog: Preventing Virtual Blight: my presentation from Web 2.0 Summit