Last Sunday morning I came in to work at just after 2:00 AM and did the upgrade on our Production Oracle system. Since I had done this a few times on our test system I was ready for anything to happen. I had already installed the new version of Oracle and so I brought the DB Down changed my $ORACLE_HOME and went to work. Launched the DBUA and saw no instances available for upgrade. I closed DBUA and went to my oratab file and I saw that my current 9 version entry was in the file. Also had some commented out instances. I tried again and had the same result. Back to oratab and I deleted all the commented entries out. Now I can see my instance in DBUA.
Let DBUA do its thing and I was done in less than 2 hours. Since I was prepared for anything, almost nothing went wrong. We have been live with Oracel 10.2.0.4 since then and have had no issue.