I just started having a similar problem and have tracked it down to an improperly secured trackpad. The left side of my pad closest to the keyboard is slightly elevated. I can push it back down and it makes a squeezing sound like its back in place but it always comes back up. After pushing it back in though its sensitivity to my finger's movement is crazy and the mouse jumps around for a minute or two until somehow it returns to normal. I have been meaning to Applecare this, but haven't gotten around to it since I need my iBook, maybe over spring break...