There is an important aspect that not many "fat clients" have solved except the iPhone (except for the fact many iPhone apps are pirated and end up torrented):

There is an important aspect that not many "fat clients" have solved except the iPhone (except for the fact many iPhone apps are pirated and end up torrented): a reliable way to charge users... 50% of Photoshop installs are pirated; I wonder how many users of Salesforce are using pirated copies?