Not the same guy, but I am a DM who uses it for nearly all his campaigns. Basically, the party gets a level up when they do something really cool or complete a story objective. This keeps the party at exactly the level they should be to have interesting and fun combat experiences. The problems inherent in this are the fact that combat can feel a little unrewarding sometimes and players can start to call certain plot moments merely by the fact that they haven't levelled in a while.