YSlow for Firebug

Just spotted (via Simon Willison's blog) that Yahoo! has released an extension for Firebug, called YSlow. The extension adds more performance data to Firebug, grading various speed issues A-F like a school exam. It seems rather cool on a brief test, though one bit did immediately stand out as potentially bad advice: YSlow suggests you should move as much Javascript as possible to the bottom of your document (to stop it slowing down your page load times). This is good advice looking purely from the angle of increasing page load times, but goes against the web standards approach of trying to keep JS out of your body code (the whole unobtrusive Javascript thing). It's not a major thing to have JS include tags in the body of your document compared to actual inline JS, but it might have been nice to see a note somewhere providing the other angle to just speed.