Jane_Doe - 3:37 pm on Apr 4, 2011 (gmt 0)
Great thoughts everyone. It does seem to indicate that the page is right on the edge of a certain aspect of their algorithm, it's just strange to me that the shift is so dramatic.
I have had the same thing happen to one of my sites. Lately it has been on page one and stayed there so I did bother to update it.
I noticed that it had some syntax issues with the html that may have caused it to have a spam penalty in the past. So the wide swings for this site may have been caused by whether they decided to penalize this type of error or not. I don't really know for sure though, but it has exhibited the same wild ranking swings like you described, over the past couple of years and especially during the past month.