I've seen individual keywords leap +50 and then go back down again between September 1 and now. I think things have finally settled out. We also lost some Feature positions that have since recovered during that time. I know in my client's niche most of the competitors are relying on static content and directories. So, I am now assuming that all has settled out, sites have been crawled and we will see more consistency in our results.
In the past 3 weeks, I have seen very rapid responsiveness to targeting new keywords. I tweaked a few older blog articles to add a few words and uploaded new articles during that time. My ranking for the added keywords showed up on the next weekly results. It makes for a nice study, but if any of the competition starts adding content, then all bets are off.