Cocoa Is My Girlfriend: "...in this post I am going to demonstrate a few things that can be done with NSError objects that have been received. Specifically, how to add options to an NSError and how to (hopefully) recover from one."
Theocacao: "The third edition of Aaron Hillegass's Cocoa Programming for Mac OS X is now shipping. I talked about it in some detail previously, but the summary is that this is one book I can easily recommend to new Mac programmers."
Both via Brent Simmons.