Apparently, Keanu Reeves gave a keynote speech at the London school of performing Arts University. A commenter at Ain't It Cool News wrote in with a few details from the keynote. It turns out that there could be a fourth (and fifth?!) Matrix film:
[Keanu Reeves says] he met the Wachowski's [sic] (no emphasis on the word brothers), for lunch over Christmas and stated that they had completed work on a two picture script treatment that would see him return to the world of the matrix as Neo. Says the brothers have met with Jim Cameron to discuss the pro's and con's of 3D and are looking to deliver something which has never been seen again. keanu stated that he still has an obligation to the fans to deliver a movie worthy of the title "The Matrix" and he swears this time that the treatment will truly revolutionise the action genre like the first movie. Wachowski's are working on a movie called "Cloud Atlas" at the moment, once that concludes they will talk again.
All I'm going to say is that, if this is true and a fourth and fifth Matrix film are each in the works, I certainly hope that the Wachowskis go back to the drawing board. The original Matrix flick was awesome -- but I cannot say the same for numbers two and three.

Here's to hoping that they take their time in making these next movies -- if indeed the rumors are true.