I don't think there are any major spoilers, most of the newspapers keep it 'spoiler-free' but with tantalizing hints. Exciting!
Yahoo News, its a hot air balloon called a Tethered Aerial Release Developed In Style.
AND, if you've read the spoilers from DigitalSpy, you'll know that "At least one previous incarnation of the Doctor makes an appearance."
Well, Several newspapers have picked this up and are claiming that all ten Doctor's will be seen in the special (although there's no actual proof of this)