n00b1 - 8:26 am on Jul 9, 2011 (gmt 0)
It added around 0.8s to my page load (taking some image-heavy pages well above 3s which I'm not comfortable with). I tested it for a week and as soon as I removed it I can see from my own testing and Google's testing that page load speed increased again.
What a load of crap. Just not worth it.