YouTube has, and this appears to be the first viable way to do it. The hack in question is similar to the one that was first used to toggle on the "high quality" mode. It is done simply by adding "&fmt=22" to the end of the video URL.
I got it to work without any problems on a video I uploaded earlier this morning. What's interesting here is that it was not ready at the same time the Flash version was.
In my case, it took about 15 minutes longer for the HD version to display. YouTube could be doing the second round of processing for these higher-resolution videos at the same time it's doing H.264 conversions for playback on TiVo digital video recorders and iPhones. My original upload was H.264 to begin with, so that could have sped things up.
Getting the higher-resolution video to display properly in embedded code is not so easy--but as you can see below, it works and looks gorgeous. You have to manually go in and change the embedded-link structure--something newbies might want to steer clear of. The YouTube embed technology for HD videos is missing the option to view in full screen, but you can toggle it on from the Google service's hosted video page.
One thing to note is that some folks to whom I sent this had problems getting the clip to display on older hardware. On my Intel Core2Duo machine, my CPU usage shot up from around 10 percent to 40 percent, and it peaked at 70 percent. This also happens on other HD video sites, such as Vimeo and Dailymotion. If you're using a computer equipped with a chip less powerful than an Intel Pentium 4, you might run into problems.