Just did the 5.6 upgrade.
Upgrade went by with only one hitch. My 3Com network adapter wouldn't work after upgrade. Short of the story is I had to go back to the machine configuration (where you set machine names, ip address etc) and reselect the network card. It had a selected 3com card, but had another 3com network card listed as an unselected option. I just selected the new one and all was well.
I just posted this in case anyone else runs into the same problem.