I recently updated my Greasemonkey script Digg Top 10 Direct at Userscripts.org to use the Digg API, and was pleased with how simple it was. One of the reasons is that its a RESTful service, which when you put the technobabble aside, means that everything works the same way a webpage does. You want to read data, you get it like a webpage; you want to write data, you post it like a web form.
I work with a lot of systems engineers and architects who will literally talk for days about Service Oriented Architecture and SOAP vs REST and get nothing done. Meanwhile, it took me less than an hour to start using the Digg API in the above script, and only an afternoon to do a much more complicated integration with the del.icio.us API for a bookmarking tool at work. When your customer cares more about working software than hot air, is it any wonder REST is pulling ahead?
