Jack Slocum has shared some sneak peak screencasts of the new Designer tool in Ext JS 3.0, and all I have to say is: coooool! It's a slick looking AIR app (built with Ext JS obviously) which lets you drag and drop UI components and data stores onto a canvas to design your UI with no real coding at all. Jack says that it is a tool that he would use himself which speaks volumes for how powerful a tool it will be.
Check it out for yourself :)