deadsea - 10:20 pm on Sep 6, 2011 (gmt 0)
I recently upgraded my server to solve capacity problems that had slowed down my site. In the following week Google started referring 15% more traffic my way.
Google's ranking algorithms are currently very sensitive to site performance. I believe that it has to do with user satisfaction being weighted heavily in the algo, not because site performance has a strong weight in the algo.