I googled this problem and found all kinds of stuff dealing with unmounting devices etc. I looked at /var/log/messages and seen that my PCI Wifi card was having an error with firmware. I am using Ethernet (eth0) for internet. When I went to MCC and opened hardware it ask to install the firmware and the shutdown hang stopped. I also checked the messages again to be sure the error went away and it did. It worked fine but the 30 second hang was a pain.
Look at the /var/log/messages log for any error and snoop around the configuration for what you find. It appears systemd likes things just right. I hope this helps some of you living with this. I just installed Mageia 2 on a SSD and that really defeated the purpose so to speak.
I almost forgot. When you shutdown or restart you have to hit the escape key repeatedly to see the messages. If you wait until the hang you will not be able to see them. This will be helpful in letting you know if this is where it hangs.