I think the major work after the launch boils down to iterating on the product (incorporating user feedback), doing excellent customer support (generates great

I think the major work after the launch boils down to iterating on the product (incorporating user feedback), doing excellent customer support (generates great Word of Mouth) and releasing new features (to keep the buzz). Also, once the initial wave of excitement goes down, what a startup needs to find is predictable source of potential customers. The medium doesn't matter as much as finding such a source. It can be affiliates, SEO, PPC or a mix of these mediums.