Some thoughts about the possibilities of API only services and Web 2 here at Joseph Scott's Blog:
Joseph Scott's Blog » API Only Services?"With open and usable APIs others are free to create entirely new 'products' by mix and matching APIs from various sources. This is great because it allows so many people to be involved in the process, not just the companies who came up with the original services. The more people involved, the bigger the pool of imagination from which new products and services can emerge."