So I am building a web application that I intend to turn into a business in the very far future. It's a pretty complex application that will take quite some time to create (in my free time too). So far I have a lot of features of the backend done (although with a lot more backend work to do).
I was prototyping the frontend and after several Jquery prototype UIs I started using Ext 3.3 for a more "final" UI. Through my experience I really like the power of Ext for the frontend and have met my first milestone (a good UI that I can use to demonstrate the product).
The original plan was to use the UI I have now as an actual basis for continued and final development. However, one thing I keep seeing over and over about Ext4 is the MVC application architecture and better data/model management. From what I am reading, this will make development and maintenance much faster and easier, something I would definitely love for this to work long-term.