Well the erratic mouse movent issue has been here ever since I first started using my G5 iMac about 5 months ago, it has been very random a day could go by and it would only occur once or twice, other days it could happen a few times an hours, but today its started to really happen very often. I had tried my MS optical explorer v4 and have also gone over to a mighty mouse but the issue remaind. I's been a real pain today as well because for the first time today I started using the my mac for some image editing where I wanted to make some changes on per pixel level, and with the mouse jumping around to the top left or right hand side of the screen I ended up with streaks/lines that had to be undone and then re-attempted. So I started reading this forum first, found a few articles and headed over to Apples websites support section, didnt find anything there about this issue, so tried their forums, where there were several suggestions for example try a different mouse mat, coincidentally I had already done this today, but the issue was exactly the same on the new one, I had also tried paper as an alternative mouse mat shortly after the issue occured the very first time but that didnt do it either. So Ive been able to get a hold of a dark plain colored mouse mat that as far as I can tell is not really physically different from the other two, other then that its a bit darker, but the issue has not come back since using this third one, I was considering zapping the PRAM as suggested by some one on apples forum but will hold off for now, if the issue comes back though I'll have to give the PRAM zapping a try.