Do not make the mistake of thinking that because my conclusion is the same as another person's that my reasoning is the same
Error messages that are useful for me but would scare the hell out of an end user
Error messages that are NOT useful for me AND would scare the hell out of an end user
Finding a bug that makes you stop what you're doing to fix it, and then restart what you're doing to take the change into account.
Establishing the line between "this needs to be tweaked" and "this needs to be fixed."