Funny I stumble on this thread, I'm going to look at one of these cars tommorrow for possible purchase.
I came across one in the past, and basically it controls everything that buttons control in normal cars. In addition to that it does stuff like automatic climate control, exterior and interior temperature gauges (celsius or fahrenheit), door ajar warnings, oil change tracking, diagnostics, compass, miles per gallon (I think), range that you have on your current gas level, and thats all I can think of right now. All radio controls are in this device as well.
Its really very cool. And it is touch screen as well.
Just hope to god it doesn't break. In addition, I'd imagine it'd be a little quirky if you installed an aftermarket CD player. I don't know what it'd do if you tried to change radio stations and such.