Receptional_Andy - 2:41 pm on Jan 6, 2010 (gmt 0)

Hi rubaducky, welcome to WebmasterWorld [webmasterworld.com] :)

There was a fairly lengthy discussion of this report a few weeks back which may be of use:

New - Keyword "Significance" in Webmaster Tools [webmasterworld.com]

Personally, I think the data provided is insignificant - although others disagree, of course.

Certainly, there seems to be post-processing applied to the data in a way that is not applied to the organic search algorithm, which may be what causing the effect you're seeing.