Ben Brooks has a good idea of what a calendar could be. His mock up looks like exactly what I'd love to see in an app. I hope someone builds it.
Real interfaces, those printed on paper for calendars, or molded out of plastic for calculators are static — computing interfaces are dynamic. The difference is that to make a sheet of paper show 7 days worth of appointments means that you have to print all seven days. Once it is past the first day it would be impossible to dynamically shift the content so that it keeps the seven forward looking days view. On the computer though this is easily done, yet no one does it — why?
This sounds to me like a great feature for a calendar. I'd love to have this on both the Mac and the iPad so that I could always see yesterday, today (highlighted somehow), and the next 5 days. Every day the calendar just shifts so that "today" is always the second one and I always have a quick view of the day before, and more importantly, a view of the next few days. I find it amazing that nobody has done a calendar application with this feature.