Enter Major Nelson and his blog of doom:
I just heard from the Dashboard team that we'll have to wait at least another day for the Dashboard update to be released. The update is not being released in the next 24-hours. That is all I know at this time, but I'll get more information tomorrow afternoon (PT) and I will update this post as needed. Thanks for your patience and understanding.
Edit: As has been pointed out by some community members, the official press release does say the 'week of May 7th' for a release time. So we're well within that so far. It sounds like some folks missed that part, so that's why I wanted to post this update.
So there you have it folks. Don't freak out if the dashboard update isn't for a day or two now. Plus, over on the Xbox Marketplace, there are two new videos showing the spring update off, the videos are available in all Xbox Live regions, and are free (shocking) to download.