According to Tim Yap's Tweet, there will be a Pacquiao-Marquez 4 based on what Bob Arum said after the match of Manny Pacquiao and Juan Manuel Marquez last Sunday. The Pacquiao-Marquez 4 might happen on May 2012.
Here's his Tweet:
To those who don't know who Tim Yap is, he is a well known celebrity in the Philippines. He has a big clout in Twitter that's why when he Tweets about something, chances are it will be viral in the internet, just like his Tweet above.