tedster - 6:21 am on Mar 13, 2011 (gmt 0)
Late last year Matt Cutts indicated in a video that page load speed was live as a ranking factor. He said it would influence about 10% of all searches in a relatively small way - as a sort of tie breaker in close call rankings.
I can't say I have any hard data to confirm this, but I also have no reason to doubt that there can be a direct effect.
The secondary ranking effects of a faster page load speed interest me a lot more. Fast sites set off a cascade of effects that can indirectly improve rankings. Happy visitors have a lot of behaviors that help improve rankings, even if it's clicking on an internal link instead of hitting the back button in frustration.