Recently I've been annoyed by the site swik.net. From the site:
SWiK.net is a SourceLabs project to help people collaboratively document open-source software.
However, it has the unfortunate sideeffect that it "masks" the real sites (because of its high pagerank). For example take this page: Ubuntu 8.10 Intrepid Ibex - Review & Tutorial. It refers to this page. However swik has a PR of 6, while the given page has a PR of 2. This means that (in Google's opinion) swik is more relevant than the original site!
What can you do? The next time swik comes up in the results too high, report them as spam. Arguably they are violating the principle "provide unique and relevant content" and are adding no value.