This received in WMT's this morning...
Big traffic change for top URL
August 2, 2013
Search results clicks for XYZ have increased significantly.
This message is not indicative of any problem in your site. It is simply to inform you that the number of clicks that one of your pages receives has increased recently. If you have just added new content, this may indicate that it has become more popular on Google. The number of clicks that your site receives from Google can change from day to day for a variety of factors, including automatic algorithm updates.
Now watch the traffic governor kick in and knock me back down.