Sometimes my mouse image on the screen stops showing. The mouse itself does still work and I can highlight an icon and click it. Just the image is missing and it makes it difficult to know where you are.
I used to have that, especially in Firefox, and it was very annoying. But it’s gone now and I don’t know what got rid of the issue. I’m on KDE 4.3.4 now, and I think Firefox has also been updated, so it could have been anything. By the time I noticed it was gone I could no longer trace back what might have changed.