I checked out the Big Brother forum on channel4.com to see what was being said about the vandalism at Uffington. Turns out the two threads that discuss it are full of people describing it as "pretty cool". Not only that, but it seems that the White Horse may be just one of five "Landmark Branding" stunts that they're doing for the new series. Loch Ness is another apparently.
Rumours are that Stonehenge is on the list.