Check out the extensive slide deck (over 500 slides) about upgrading techniques to Oracle 11.2, by Oracle Corp (Roy Swonger and Mike Dietrich):
It has lots of examples (from real customer upgrade cases) in it.
Thanks to Randolf Geist for telling me about this.
You can also download other interesting presentations from that page (check the right hand side download section), like the Oracle Database Behavior Changes 8.0 through 11.2 doc. Pretty cool!