Matt Cutts says “Nooooooo” and wishes he could come through the screen and press your ESC key and Ctrl C and Break, funny guy :-)  (he actually is).

What I how ever heard was that they are using other means that the Googlebot to look at sites and evaluate the page speed, what he does not say. I also believe that when Google comes in it’s not downloading all the images and javascripts, CSS and so on, Googlebot looks at the content so having good HTML might actually be more important than cloaking content.

According to Mr. Cutts the bottom line is that if you do serve Google one type of content and the user other, it’s cloaking and the “Noooooo” was for that reason. So don’t serve Googlebot content-only (cloak) pages optimized for load speed.