Sam - thanks for sharing that.
My own thoughts looking at your graph and if I'm understanding it correctly are that for your site there's something other than Penguin going.
Looks like you were already on the downward trend before the Penguin strike on the 24th/25th. In fact Penguin seems to mark the start of your recovery.
I agreed at first. However, reflecting on main post too, it seems google did a number of big changes before 24th - the big day - which affected my site. I can grab a longer distance shot of the visits, as that one obviously only shows a month, but thats because that is the standard for google analytics. Also, I've had these results become the majority result - the "update" causing success after fluctuations before. Has anyone else had like wise?