Unfortunately, much of the discussion about the Mayweather vs. UFC PPV war this evening has focused on absolute numbers instead of addressing the context. Mayweather's fight should destroy the UFC card tonight; anything less would be a huge disappointment considering the circumstances.
UFC 103 is the weakest UFC PPV card of the year in terms of star power. Franklin is a name but not a drawing card, Vitor Belfort means nothing to the current fanbase, most people have no idea who Junior Dos Santos is, and Martin Kampmann doesn't draw any extra buys beyond his immediate family. Unless the huge amount of viewers that Kimbo Slice brought in Wednesday night decided to buy this show, it should do around 325,000 buys.
On the other hand, the Mayweather vs. Marquez fight is one of the few boxing PPV shows of 2009. HBO responded to low numbers at the end of 2008 by reducing the amount of PPV shows in 2009. The UFC took the opposite approach and actually increased the amount of shows they made fans pay for. The UFC is on pace for a watershed year, but at the same time fans are taking a span of weak cards as an opportunity to save money and wait for the big shows at the end of the year.
The talk that Mayweather isn't a draw on his own is ludicrous. Hatton was not a big name in the U.S. before he fought Mayweather, and they did a fantastic buyrate together. It would be one thing if boxing fans were being killed by PPV bills every month, but they aren't, and there's no way they are going to skip out on one of the big fights of the year, even if there are a lot of questions surrounding it.
Ironically, this "competition" is a lot like Mayweather vs. Marquez. There's one extremely likely outcome, and a bunch of smoke and mirrors to make it seem like an even contest. It's not just "boxing guys" misleading people, Dana does it too all the time. Next month when more people see Randy Couture vs. Brandon Vera than Manny Pacquiao vs. Miguel Cotto, Dana will probably claim an equally meaningless victory.
Unless Kimbo Slice changed everything, I think Mayweather vs. Marquez will draw 600,000-800,000 buys, and UFC 103 will draw 300,000-350,000 buys.