tantalus - 6:18 pm on Mar 20, 2012 (gmt 0)
The tracking software I use on a site of mine tells me the #position the keyword is in when clicked on. Checking the SERP myself I rank #9 for a major keyword phrase. However, I never have clicks on this position. My clicks come in at positions 11, 12, 14, 15, 18, 20, 21, and 22. I cannot figure out what real position I rank for. This has been happening for a couple of days. Before this I ranked #12 when checking the SERP myself and I was getting clicks at that position according to the tracking software. But, I was not getting very many clicks that I would expect at that position. Now I am getting more clicks even though my position is fluctuating wildly.
I was reading daveN last night about the integration of localisation into the serps (without maps) recently, and their quoting it as "The Biggest Change In SEO To Date"
Could be your fluctuation is due the location of the searcher, and the number of local companies available in the area to list in the serps. I don't know if your specific industry would trigger this kinda of thing though.
I noticed alot of flux in the UK serps last night and popped to see if that was the case. Seems confirmed, somethings going on.