Same problem here. Upgraded from F16 to F17 (XFCE spin) using PreUpgrade on a Thinkpad T520. Very easy to consistently reproduce using any open window, or even just an XFCE panel.
Using just the XFCE pane:
1. Click the XFCE applications menu button on the panel (cursor disappears)
2. Move mouse away from the application menu that pops up during #1 (cursor reappears)
3. Click empty space on the desktop (cursor disappears)
Using an open window:
1. Click empty space on the desktop until your cursor is visible
2. Click any open window to bring it into focus (cursor disappears)
3. Move the cursor over the desktop without clicking (cursor reappears)
4. Click empty space on the desktop (cursor disappears)
5. Repeat from step 2
It also seems to happen pretty easily if you just use the mouse scroll wheel to scroll the contents of any open window with a scrollbar enabled. Keep the mouse still, use the scroll wheel in any direction, cursor disappears.
I've also noticed the cursor tends to disappears during the transition between icon states. For instance, from the normal cursor to the text selection cursor when hovering over a text field. If you move the cursor very slowly, it'll disappear right at the transition threshold.
Very annoying to say the least. It's so annoying I am considering a fresh reinstall and considering the upgrade botched.
EDIT: I've found another thread which seems related: http://forums.fedoraforum.org/showthread.php?p=1584509