There was much talk about UFC 136 not drawing a ton of casual interest. At least in terms of the UFC 136 prelims on Spike TV that is looking to have been the case.
The preliminary broadcast, featuring Anthony Pettis vs. Jeremy Stephens and Demian Maia vs. Jorge Santiago, drew an all time series low of one million viewers (household rating of 0.8) according to Spike TV. For comparison, the last prelim broadcast (UFC 135) drew 1.6 million. The 135 bouts were much weaker by comparison given that Pettis, Stephens and Maia are long time Zuffa properties who have been featured for their bouts in the past.
There isn't an exact ratio of Spike viewers to PPV buyers, but it's never a good thing to have a low rating for the lead-in broadcast.
It'll be a very big shame if the numbers carry over the the PPV buys given just how enjoyable the main card was.