For some unknown reason, I’m jonsing to try Omnifocus, the online GTD system of choice for Mac users. That said, my own Moleskine-based GTD system works just fine already. There are certainly advantages to the digital system including easy refactoring of projects and actions and delaying actions until you actually want them to show up in your path. It was these advantages that got me to drop the $80 for it.
Mike’s cases for OmniFocus and for a Moleskine-based system are great.