There hasn't been any information leaked as to what it will be but the page with the timer has the following statement around the clock, "So close, you can almost touch it." Which leads me to believe they are releasing a "touch" enabled device to the public.
With the Unity interface already appearing as a touch friendly interface, I would not be surprised to see Ubuntu on mobile and tablets within the very near future. In fact, back in late 2011, Mark Shuttleworth, who is the owner of Canonical, stated in a blog, "By spring of 2014, version 14.04 LTS "will power tablets, phones, and smart screens from the car to the office kitchen, and it will connect those devices cleanly and seemlessly to the desktop, ther server, and the cloud."
What do you think will be revealed in less then an hours time by Ubuntu?
UPDATE: Ubuntu for phones is what the announcement was. You can learn more about it HERE. I suggest you watch this awesome video to learn more about Ubuntu being on ALL devices eventually. It's a virtual keynote speech by Mark Shuttleworth.