macdave - 4:30 pm on Aug 15, 2005 (gmt 0)
While Google will probably never admit to it, the post-Bourbon adjustments appear to have been largely driven by human reivew. Most affected have been sites that experienced big drops or gains during the Allegra and Bourbon algo updates. In all likelyhood there is now an algo that's flagging borderline sites for human review and, in some cases, applying a temporary penality. (Pages dropping from first page to position 160-170 is a common trend.) Sites are then reviewed and black- or white-listed (or maybe they get a quality score that's used as a weighting in search results). The updates that we've seen over the past few weeks appear to reflect batches of those judgements going into production. A very important point to note is that these changes have affected entire sites rather than individual pages.