Now that mockup I like -
Not really functional - it's like a digital bento box, but nice to look at for a bit.
I think one of the first huge selling apps we'll see is the Trekkie tablet app! Seriously - someone could make a mint from providing key information through a Star Trek like UI.
Watching the changes over time in iTunes is seeing it morph to Tablet friendly - A lot of the content now being viewable well with a 10" screen in landscape.
E.g. The STORE section, iTunes store - the top header rotating ads section - The whole picture = the hyperlink. To the right, big chunky pictures to click with a finger. Same with the Music section below - The cover art and the text = link, with a nice multitouch 2 finger gesture just sliding that 2 rows of albums along.
This might be barking up the wrong tree, but irrespective of that likely possibility, - If you reduce the width of iTunes on the iTunes store page, the width is akin to what it would be for a 10" screen it seems. I imagine there's a sweet spot they'd normally go for to look good on monitors anyhow, but it is curious to watch the design of the site progress.