[warfangle]

Having to ship your code back to the mothership to run unit tests made it impossible to run TDD (~30 second overhead on each test run). That along with the test coverage requirements made it a pain on the first level. Unless you're using their utterly abysmal in-browser editor.

On the second level is if you're building an app that needs to talk bidirectionally to salesforce on a per customer (app install) basis. Each salesforce site has their own WSDL URLs. That makes sense if all you're doing is building something out for your own Salesforce site.

But if you're building something installable over their marketplace .... it's almost impossible to have a seamless user experience, from the customer's point of view.