When Apple introduced iPad, they let it run pretty much every iOS app made for iPhone and iPod touch (absent camera and phone apps, of course) by boxing them or pixel doubling them. Depending on the exact nature of the app, however, the experience at 1024x768 and 9.7-inches varied from fine to dismal. Luckily there were 5000 or so iPad specific apps available at launch and that number has continued to grow.
Now iPhone 4 -- and likely soon iPod touch 4 -- have 960x640 displays but still only 3.5-inches. If iPad was a step up, iTV will be a leap. There's an outside chance of 1920x1080 or the current 1280x720, both of which are probably workable just like they were for iPad... except TV screens won't be multitouch and they won't be in our hands or on our laps.
What made the 2007 iPhone a breakaway hit, what let it change the industry was its multitouch user interface. It disintermediated physical keyboards and styluses and let us touch and directly manipulate the UI.
Sitting 10 feet away, far removed from 30 to 70-inch screens, acting through some type of remote, wand, scroller, trackpad, or iPhone, iPod touch, or iPad, what kind of apps make the most sense?
I can see a few categories.
While iPad is often labeled a consumption device, iTV would be even more consumption oriented. You probably wouldn't want to even try to knock out large docs or use complex productivity apps. It would be a grosser, more distant experience. But absorbing media and entertainment, information and analytics could be fantastic. Those are the types of apps I want to see.
How about you?