Last weekend we upgraded our EBS environment. 12.0.6 to 12.1.2, 10g DB to 11gR2 and migrating to a 64bit server. I started 2pm on Friday and finished 6am Monday morning. During that time I slept for a grand total of 9 hours. I only hit one major issue during the upgrade which required opening a P1 SR with Oracle. It took about 3 hrs to resolve, would have been quicker but my analyst went to lunch!
The other other issue was performance. Our DEV server crash and burned a couple of months ago, so the networking guys gave us a loaner. It didn't even cross my mind to check the specs and compare it to our production hardware before I did a dry run to work out the timings. I managed to shave 18 hrs off the upgrade, which I assumed was because of a few changes such as applying the patches with nocompiledb,nocompilejsp,noautocfg. I expected the 12.1.1 patch to finish around 2am on Saturday morning. 2am came and went with the patch still running.... 3am, 5am, 7am, finally 8am it finished!
I couldn't find any significant performance issues so I looked into the server itself. It turns out, the loaner server is twice as powerful as our prod! I should have realized it during my dry run, but I was so busy I didn't have time to investigate. With 2 major upgrades back to back the last few weeks have been crazy.
Well, all done now, environment has gone live and I haven't heard of any major issues. I did have issues cloning and will put up a post on that shortly.