There are many articles claiming to have valuable insight for webmasters trying to understand how search engine's rank there sites. This study actually is pretty interesting. They claim inbound link quality (not quantity) is the most important "off-page" factor (factors other than the page itself). And in, fact inbound link quality is 42 times more important than link quantity.
Inbound link relevance is next at 11.6 times more important than link quantity (which shows how important link quality is).