This is a very interesting and perplexing situation. Sent this question to many people but they could not spot the dot. On the 9th of January 2011 the search query impressions for a site that i analyse just went through the roof. Maybe not that hig but from an approx of 400 impressions to 2400 impressions with the click rate change or the traffic changing must be something really not right. I sent it around through a lot of forums but i dont think people could get a descent understanding so i decided to upload it into a post. Below is a clipping from webmaster tools indicating the spike in traffic.
As you can see below the clicks to impression is in somewhat of a relation. and the previous part of the graph has been the same.
I also have here a clipping from google analytics showing no particular increase in traffic that should have generically been caused by the spike in impressions as can be seen below.
Out of all the amazing things i did during this period one of them was uploading about 70 products to the online shop. But these products were only indexed as of today. Another thing was our monthly newsletter but that went out on the last day of the graph being the 13th. So nothing really visible to me. Uploaded this in the hope that somebody would have the answer to this.