So... I made a quick benchmark with script positioning, and here are my (non-scientific) results:
- all browsers pretty much execute the stuff in the same time. So the time before .load() is available remains the same, whatever the method used.
- IE6 benefits from having scripts at the bottom, because it's so slow at executing JS, and running jQuery + script in the head slows it down by a second or two... :( So, I've disabled it for IE6, it'll always execute below.
- IE7, IE8 and IE9 give similar results in both situations.
- Same for Chrome, Firefox 3 and Safari.
- Opera looks clearly better with the scripts at the top, plus it probably fixes the occasional FOUC I would get (only in admin pages). So it's definitely staying this way for Opera (i.e. always at the bottom, except if user is logged in and came recently.)
Interestingly, the YSlow tool recommends having the scripts at the bottom -- but wherever I have them, it still gives me an A ranking for that category. It probably 'understands' that some scripts can't be put at the bottom (which is actually completely untrue, given what I managed to do with SMF/Wedge, but whatever.)