I work in a design office and myself and another designer are suffering from this problem.
Reading through the posts this is seemingly total random, for us it only happens when using photoshop with the main cursor randomly disapears on our principal screen. We dont have Crhome installed and from reading the post I see different theries as why this is happeninh, but sadly not many are common. I was intially lead here from the Adobe forum as I thought it was a photoshop issue but now Im not so sure ?
We both have 2 monitors set up, myself 2 apple monitors and my collegue a Lacie and some random moniotr that I cant remember now. We're both using G5 towers with 10.7.5 and adobe creative suite 5 installed, only happens when using photoshop, thats to say we use illsutrator every day and it never happens there.
I install the photoshop CS6 beta a while back and had the same issue, I have since uninstalled it.
On a side note, for us at least, to get the cusor back we just have to click randomly on the second screen making sure to leave photoshop (so basically clikc on the desktop of the second screen) and then click back into photoshop.
Would be really interested to hear from more 10.8 ML users on this to see if anyone had the problem resolved that way, we can easily upgrade if needs be but it's not really worth it if the problem hasnt been fixed.