Plus, Matt Cutts recently said at Pubcon that Google now analyzes the content which it decides is above the fold, and places a higher value on that content in terms of determining SEO results.
I completely agree that we shouldn't stuff the top of the page with every important pieces of content and navigation option to the point where it makes the page a mess. But at the same time you can't treat a really long page as if the content in the middle or bottom gets the same attention as the content at the top.