When using Zoom (Meta-+, Meta--, Meta-0), then going back to 100%, my mouse cursor disappears.
Work-around: Use Ctrl-Alt-Del to logout; the mouse cursor reappears; login.
This solved it:
Menu | System Settings | Desktop Effects | All Effects tab
Click on Zoom wrench icon to get Zoom dialog.
Check Enable Focus Tracking checkbox.
Click OK button.
(The other work-around was to disable, then re-enable desktop effects, which are toggled with Alt-Shift-F12.)