I do ExtJS allll-daaay long, because my company built every back-office we made upon that framework. Pro: It looks and feels like a desktop application. B2B loves that! (And that's why we use it) Cons: It requires you to write gigantic blocks of code to get something up and running. + Many times you will say to yourself "they can't have forgotten THAT feature", and well, they did and you have to DIY