Dave Meltzer has a very interesting bit in this week's observer about Vince McMahon's role in the growth of MMA.
When The Ultimate Fighter debuted on Spike, it came on at 11 after Raw. It was a perfect lead in for the UFC. Apparently WWE had a no-compete clause with Spike that applied to UFC, and Spike needed Vince to approve TUF to put it on. He did approve it, and the rest is history.
Next to the XFL debacle, this has to be Vince's biggest mistake of the last 15 years. His domestic PPV numbers have crumbled in the last two years, corresponding with the incredible rise in UFC numbers.