Google states that their ranking algorithm uses over 200 factors and updates are made at a rate of 500-600 per year. They’re using that statement to defend themselves against allegations they’re favoring their own resources in the search results. That statement doesn’t really defend anything though… surely, one of those factors could be “if site belongs to Google, boost by ten million”. I’m such a cynical bastard.
Changes to the algorithm at a rate of 500-600 per year wasn’t always that way though. Back in 2003, Google only planned to update the algorithm once a month. The updates were given christian names from the webmaster community like they were hurricanes. They certainly caused a storm of activity every time as websites strived to avoid the ban-hammer and achieve new rankings. Particularly, when the updates cottoned on to archaic and stupid techniques like hidden text and keyword stuffing.
Anyhow, this is just a short post because there is thunder here, and I don’t want to steal it. That awesome SEO resource, SEOMoz.org, has put together a fantastic page on all the major updates made to the Google algorithm since 2000. Things like Panda, Cassandra, Vince and Boston. Check it out here.