Maybe I'm misinterpreting something, but the way I understand it, the last (or only) page of a website is handled differently. If it's a single page website with a demo download, and someone downloads the demo, then the time between pageload and the download would be counted. If there's a Flash movie, the time between loading the page and playing the movie would be counted. It also looks like you can come up with your own custom events to track, maybe like clicking an outgoing link?

I've never seriously used GA so take my interpretation with a basketball-sized grain of salt.