Dave Meltzer reports (subscription required):

Early reports on UFC 113 on 5/8 in Montreal have the show doing 520,000 buys, slightly above the 450,000 that the first Lyoto Machida vs. Mauricio "Shogun" Rua fight did. We should note that there were cable reports as high as 687,000 for the show, and trending patterns were only slightly behind GSP vs. Dan Hardy and the highest besides that show since August, which would also indicate something closer to the latter than the former. There are a lot of other measures that also indicate the higher number, but as far as the number of buys from people who would have the numbers and that can be confirmed, the lower number is the best number we've got.

MMA Payout adds:

I've been harping on how PPV buyrates go in cycles and that we were coming up on a big cycle in March. If UFC 114 performs as we all expect it will, the string of events from UFC 111-114 will be the first four-event string in UFC history to sell more than 500k at each event. It won't be the most lucrative series in UFC history (that still belongs to UFC 97-UFC 101), but it's still a feather in the UFC's cap, especially in light of all the people that said the UFC had peaked.

I don't expect the UFC will make it five in a row with UFC 115, but the UFC is rolling out the movie theaters for the event which suggests they're looking to give 115 a little extra support (fight week promotion could push that event over the top). However, if the UFC can push 115 above the 500k mark, it should be good to establish a record string of events with 116, 117, and 118 this summer (Lesnar-Carwin, Silva-Sonnen, Edgar-Penn/Couture-Toney).

In fact, the way things are shaping up right now, the UFC could end up beating its mark for PPV buys from last year - something that's pretty impressive considering they had a very bad start to the year.

MMA Mania has a different take:

If the numbers end up being around 520,000 or so, you'd have to think it would be a bit of a disappointment for the UFC. Many industry insiders estimated that UFC 113 would fall in between the 600,000 - 750,000 PPV buy range. It may speak to several items, most notably of which is that Kimbo Slice's drawing power doesn't translate to pay-per-view as well as it does network television, in turn, more than justifying the UFC's decision to release him.

All told, the UFC continues to do very good business in a down economy, but they have failed to blow the roof off and continue the pattern of explosive growth that they flirted with in 2009. They really failed to make the most of Kimbo Slice, perhaps that's to their credit, but nonetheless, they certainly underplayed his PPV debut.