Dave Meltzer has the early PPV estimates at the Wrestling Observer (subscription only):

The Spike prelims did a 1.03 rating and 1.54 million viewers, the third best number out of the 12 similar shows in history, after doing low end numbers the past several fights. The show did a 1.42 in both Males 18-34 and 35-49.

The earliest PPV numbers, which this early in the game is at best a rough estimate, is slightly more than 1 million, putting it in the same range as all the biggest events in company history except UFC 100. 

He also has some theories about why it did so well:

The marketing drew an interesting reaction. The commercials played so often that within the Mexican-American community, and outside it as well, people who didn't know Velasquez, didn't follow UFC, and some of whom didn't even know Lesnar, knew about a Mexican trying to be the first world heavyweight champion. The awareness of this show was huge. Many people who have never seen UFC were interested. The reaction at bars and theaters, most, but not all, of which drew numbers like the biggest UFC events to date, was how many Mexican Americans were in the place, a demographic UFC had been trying without a lot of success to hit-since that audience so strongly supports boxing and pro wrestling. A wise old booker with decades of watching the business named Dory Funk Jr. told me nearly 30 years ago about drawing minorities to wrestling, that also works with combat sports. The idea of drawing a minority group by putting people from that group on the card means nothing. Unless they are in the top position, it's not going to click. People want to support their champions, not just see the people they can relate to be on the show. UFC tried with Roger Huerta, and it didn't work even though he looked like a star, talked like a star and had a marketable life story, because he wasn't able to get to championship level. Tito Ortiz tried, but never connected because there was a certain phoniness to his approach.

The marketing clearly worked for this show. How big a star, a draw and a hero to Mexican-Americans Velasquez can be depends on a number of factors, based on a combination of how he handles the rough road of instant success, and where his title reign goes from here.

Jamie Penick of MMA Torch comments:

It's not surprising in the least with how well the Primetime shows performed and with how much press there was for the fight. I think it will ultimately surpass all but UFC 116 and UFC 100, but it could also sneak into the second place spot. The UFC may have trouble reaching a million again outside of the GSP-Josh Koscheck fight in December for awhile with Lesnar's loss, but at the same time Velasquez can be built into a bigger star himself if he can keep winning fights in the manner he's been doing. The UFC will set break the pay-per-view record again this year, but may have a tougher time in matching it in 2011. Only time will tell on that front.

Basically with Brock Lesnar no longer the Heavyweight champion, he won't be turbo-charging their growth rate any more. It's a long term bet on Velasquez, but it will take several title defenses, preferably in spectacular fashion, before he can build his initial success with the Hispanic demographic into a major draw. 

If Georges St. Pierre loses to Josh Koscheck at UFC 124, the UFC will have lost their second most popular champion in a matter of six weeks since losing their most popular champ. Fortunately they've always marketed the brand first, not any individual star. 

My prediction is that the UFC enters an era of consolidation where they maintain current levels of success, continue to expand internationally, make huge profits and continue to make inroads into the American sports mainstream but the days of hyper-growth are over.

That's assuming they don't develop another break out star in the next six months. It's MMA ,anything's possible.