If you have upgraded or installed Fedora Core 11, you might find that your USB ports are not listed or the Serial Port menu is greyed out on the Arduino IDE. This is due to a change of group ownership for the /dev/ttyUSBx ports in FC11.
To resolve this, simply add your user (eg. myuser) to the dialout group in /etc/group like this:
Then logout from your desktop and re-login back again.