I don't know how many of you read Merlin Mann's blog, but I often pick up some pretty useful stuff from him. Here's one. It's a good primer for those of you just starting out with GTD (and OmniFocus), as well as a good reminder for the rest of us.
http://www.43folders.com/2008/08/08/outcome-based
http://www.43folders.com/2008/08/08/outcome-based