I don't know if it was ever confirmed or not, but my thought about who Yoda heard during his meditation after Anakin slaughters the Tusken camp turns out to be true. I turned on the subtitles during this scene, and sure enough, the following appeared: [Qui-Gon Jinn's voice] Anakin! Anakin! Nooooooo! Why do you suppose this happens? I would say it's the Spirit of Qui-Gon expressing his anguish over Anakin's brief "turn" to the Dark side. However, there's all that business about Qui-Gon not "becoming one with the Force" when his body doesn't fade away when he dies. So, what do you think?