Today I bring you several articles from Oracle about bugs and upgrading! Starting out with "Things to Consider Before Upgrading to 188.8.131.52 to Avoid Poor Performance or Wrong Results" with note ID 1392633.1, we also have note ID 1320966.1 for 184.108.40.206.x versions, and 1645862.1 for 220.127.116.11 versions. Pick your poison for what version you are on or are planning on going to some day!
Going a step further, I tried to search My Oracle Support for "Things to Consider Before Upgrading to 12.0" and "Things to Consider Before Upgrading to 10" yet, for some reason I do not understand, I was redirected to "Oracle Support Lifecycle Advisors" note ID 250.2 but nothing here shows up about what I searched for. Still, you may find that article to be of some interest anyways!