dickbaker - 11:30 pm on Mar 13, 2011 (gmt 0)
Several websites I have worked with have seen significant conversion and subsequent revenue increases by making speed changes that most webmasters would deem unnecessary.
I've increased my page speed to anywhere between 83 and 91, but my rankings haven't changed. In fact, I was hit hard by the Panda update, so page speed isn't a factor right now. Maybe it will be when all of the other changes are made.