The day the week starts
One thing I really love about modern programs with any sort of calendar element: I get to choose the day the week starts. No longer do I have to put up with some of my calendars starting on Monday and some starting on Sunday, depending on what country developed them. No longer do I have to scan opposite ends of two different lines to find out what I'm up to on a particular weekend (which is the majority of my calendar usage). Fabulous!