google webmaster tools bug
June 9th, 2010barry beat me to blogging this as I’m far to busy so credit to him for picking up on it.
You can see his post here: http://www.seroundtable.com/archives/022347.html
When he wrote about it the screen grab he had didn’t show this bug so I sent him one from a site of mine.
Here is the drop is click and impression according to google webmaster tools:
And here is a screen shot of traffic:
Bit of a google bug 
I think that analytics where not the only one affected , google adsense click count might be too. I noticed a click count drop. I dont really know if this two are related…