I highly recommend for everyone to check out Seomoz.org if you haven't before. And particular a recent article by CEO Rand Fishking about how Google's Rankings Algorithm Has Changed Over Time
This is awesome. Thanks Rebecca. I've always known about Google changing up its algorithms, but it is great to see all the different variables laid out graphically to see how they change over time.
I wonder if any marketing experts that are more experienced in SEO than myself are brave enough to make predictions on how the ratios will change in the next few years.