Early estimates have UFC 133 trending at 310,000 buys, according to Dave Meltzer of the Wrestling Observer(subscription required). That number continues the trend of disappointment that has plagued 2011 thus far.
High-end estimates for 2011 PPVs (info from Wikipedia):
The UFC pulled in 9.3 million buys in 2010. We're almost through August, and they're sitting at 3.6 million buys in 2011. There's no simple explanation to data fluctuation, but the rash of injuries at the top of cards -- most notably the absence of Brock Lesnar for the entire year -- is a major factor.
The UFC has a fantastic lineup set for the fall and winter -- Jon Jones vs. Quinton Jackson at UFC 135, Georges St. Pierre vs. Nick Diaz at UFC 137, and Cain Velasquez vs. Junior dos Santos at UFC 139, but it's unlikely those shows make up for lost ground.
This also isn't great news for Rashad Evans, who continues to prove that he can't draw without some serious support around him. His history as a main eventer:
UFC 114 - 1,050,000
UFC 108 - 300,000
UFC 98 - 635,000
UFC 92 - 1,000,000
UFC 88 - 480,000
UFC 78 - 400,000
UFC 98 is arguably Evans' most impressive performance as a PPV draw. UFC 92 was a year-end mega-show featuring an interim heavyweight title fight and Ultimate Fighter conclusion plus a trilogy fight between "Rampage" Jackson and Wanderlei Silva. UFC 114 was built on a well-hyped season of TUF, and the artificial drama created by "Rampage" putting the fight off to do promotional work for the A-Team movie.
At UFC 98, Evans' title defense against Lyoto Machida was the bulk of the draw. (Though Matt Hughes and Matt Serra were settling a TUF feud of their own.) Machida had never appeared in the main event of any UFC show, let alone a PPV.