ExpressionEngine Upgrade Errors Guide
There’s a new wiki page to assist you in addressing issues when upgrading ExpressionEngine. It provides some troubleshooting tips with everything from server requirements to MySQL errors.
If you experience an upgrade error when upgrading ExpressionEngine from either EE 1 or EE 2 to the latest version of EE 2, this guide will help you walk through some troubleshooting techniques to get you back up and running.
The guide was put together by Kevin Smith and looks like a great resource. Perhaps it should be included in the official documentation. Either way, bookmark it!
Read the guide: Troubleshooting Upgrade Errors