As I said, I would bet a large sum of money on Mayweather winning a comfortable UD, though I could see Pacquiao taking a few rounds.
Have negotiations started yet for this fight? This whole thread got me excited for the fight already.
Pacquiao right now is more battle ready than Mayweather. The Marquez fight didn't do much for Mayweather in terms of ring rust that he barely showed, but my concern for Mayweather is the fact that he hasn't fought anyone with the skills of Pacquiao. Floyd will lose this fight if he fails to give Manny any credit for his boxing skilss. Floyd will win he focuses now on his game plan and prepares himself business as usual. I still believe Floyd's quickness and accuracy would carry him to a UD, but I wouldn't be surprised if the judges favoured Pacquiao's pressure and workrate, winning him a close, maybe split decision over Floyd.
These are my thoughts as well. Floyd would likely win a boxing match, but I'm less sure he'd win a fight between the two and I think Pacquiao would go out on his shield before not doing everything possible to turn it into a fight. That said Floyd does have a noticable size and speed advantage, I just don't think he enjoys having to go into the trenches and I'd say the key would be whether or not Pacquiao could consistently land bodyshots, which over time would slow Floyd down and hurt like hell.