It's called "negative seo" and it does appear to be an effective way to blast people out of Google's top results. Here's a comment I found from someone else who's experienced this: http://www.seobook.com/negative-seo-outing#45906
http://www.seomoz.org/blog/negative-seo-myths-realities-and-...
In the seomoz article find "It's even more terrifying, but they sent fake emails" to get to the relevant part.