We find XML RPC via HTTP to be very compelling. It has essentially, and quickly, become a core focus of our company. This protocol along with great scripting tools, and some wonderful products like REALbasic are enabling us to build small, lightweight, purpose built apps. They tie into powerful backends like databases and Frontier .
Development is extremely rapid.
We produce apps with extremely clean interfaces. They are short and to the point. True thin clients. Our apps have required about ten minutes of user training, and users have built entire websites after that training with virtually no knowledge of how websites are built. Have a look at Archipelago our latest effort.