I also saw a tutorial on YouTube that showed a separate window with a computer monitor a tablet and smartphone for CSS layouts...
That is the Fluid Grid Layouts feature for building Responsive Web layouts. Below is a live example, resize your viewport to see it work.
CS5.5 has easy tools for inserting rollovers, however it is now better practice to use CSS instead of JavaScript that is automatically generated.
CS6 still supports rollover Behaviors. Nothing's changed there. I don't know if CSS is really "better" than JavaScript. I think it depends on your target audience and what you're trying to achieve.
Nancy O.