Apple have it right with their App Store. Salesforce.com are making money from force.com, Google Apps ditto. What do all of these have in common?
Platforms, platforms, platforms, platforms. I think the future of monetization on the web will be in platforms that can deliver a rich application ecosystem. People will pay for applications that are priced right and deliver functionality (or frivolity). Each of these platforms of course have a unique value proposition - mobility for the App Store, social graph for Facebook, useability for Google Apps, business productivity for Salesforce. Certainly, every mobile vendor under the sun now has an app store.
I recently paid $70 for a GPS app on the iPhone. Why? Because I didn't have a GPS and it made sense to purchase a $70 app rather than another $300 gadget. There is no reason why I wouldn't pay for the right app at the right price on Facebook.