Just playing around on the official site, the countdown page, and something happened that hasn't happened before (I think)
I right-clicked on the clock and pressed forward on the pop-up menu... and it took me to http://rockstargames.com/IV/index2.html
... whereas before I think it restarted the clock? Can't remember.
But this probably means everything, the site, the trailer etc. is already uploaded and ready to go, and all they need is the go-ahead on D-Day to make it viewable to the public... Which may dispell rumours of the trailer taking a half hour for them to load up on the site.