The Official Google Blog has an occasional series, search quality, which contains information which could be useful to us as SEO's.

Some of the more useful posts in the series:

Official Google Blog: Introduction to Google Search Quality
Official Google Blog: Introduction to Google Ranking
Official Google Blog: Technologies behind Google ranking
Official Google Blog: Search quality, continued
Official Google Blog: Search experiments, large and small
Official Google Blog: Search evaluation at Google

Here is a good white paper written by Amit Singhal, one of the Google Fellows, Modern Information Retrieval: A Brief Overview.

And here is a series of mostly relevant videos, Google Roundtable.