Two interesting posts for anyone considering building an application on a hosted platform like force.com (Salesforce). Onstartups has a thoughtful article about what it would be like to succeed on such a platform, and how much money and control you might end up ceding to the hosting vendor. Bob Warfield’s Smoothspan blog takes up the theme with a response that is longer than the original. What does it all boil down to? This, I think (from Smoothspan):

First, it has to be possible for you to move your software in a reasonable amount of time to new lodging if it gets too ugly.

As Smoothspan notes, this is what makes a service like Amazon S3, which you can easily switch out for another service, more attractive from this point of view than force.com, with its proprietary Apex language and forms.

That does not mean force.com is necessarily a bad deal. It means there has to be a lot of added value – such as productivity, high-level components, rich services – before it makes business sense to accept the lock-in.