Over the last 2 years, I've watched my business go from the 4th page of results for important searches, to always ranking as #2-4 on page 1. More than anything else, what made the difference was time. In my experience, Google heavily rewards old backlinks and old websites -- much more than it used to around 2005. Maybe it's an anti-spam technique, since age is a hard thing for black hat SEOs to fake.