According to a "trusted source connected to the matter", some of Sony's internal development studios are in the preliminary stages of building projects intended for the PlayStation 4. The source was unable to confirm to Develop which of Sony's sixteen internal studios were working on such projects.
If the projects are only in the preliminary stages, odds are that the PS4 is still a few years off, leaving plenty of time for the PlayStation 3 to continue to grow, and for Sony to spend at least a couple years putting a stronger focus into the PlayStation Vita.
Industry analysts, various publishers, even Sony, dismiss the idea of a PS4 any time before 2014. The PlayStation 3 is still considered a powerful machine, with ample room left for developers to squeeze out more and more performance.
One thing is for certain: The PS4 won't stand a chance next to the GameRevolution WiiPlayBox.