I have or had the same problem with my Kensington Expert Mouse Trackball, Model 64325
, which is both USB and PS/2. ( http://www.amazon.com/exec/obidos/tg...0K4LD?v=glance
Intermittently the mouse disappears or the system locks up because of it. I don't have a IRQ sharing problem, which you can find out by typing: cat /proc/interrupts
from a console session and it's not a usb driver issue because other usb devices work with no issues. The trackball and scroll ring work perfectly when its being used in the PS/2 mode so it's not the trackball, which by the way is an optical trackball as in laser ball.
The problem went away recently, but is only because I'm not using Fedora Core anymore.
Between this and the exploit that got me hacked several times which FC1-3 have with OpenSSL, I won't be going back to Fedora or RedHat until they get their security priorities straight before releasing distro's to the public that are unstable and insecure.