With the platform's Ajax capabilities, it is possible to fairly fluently react to user interaction with a page, but there's always a slight lag for calling back to the server. In many cases, it wouldn't be needed at all to do a server call back, for example in case of OnChanges that calculate something based on the value modifed. Only when performing database access it would be truely needed to go back to the server. Therefore I propose client-side actions. Those are just like normal actions / screen actions, with some restructions like no database access, that are not compiled to Java or .NET, but to JavaScript/jQuery. Having such actions would greatly increase the speed of interaction.
Additonally, when the platform has a compile-to-JavaScript, we could create client-side widgets that directly interact with the screen, comparable to the many widgets that basically consist of a lot of JavaScript/jQuery that can be found in RichWidgets and the Forge. This would greatly ease the development of such widgets, and wouldn't need specific JavaScript knowledge.