Just did a little over 1,400 miles in two days in our Mini. Being 6'1" tall I was a little apprehensive about the comfort level but at the end of each day it was fine.
Great leg room and wasn't any more or less tired than when making the same trip in our large SUV. Averaged almost 37mpg on the whole trip going around 75mph. Great transportation! Of course this was the first experience in temps below 35 degrees so the second day got the low air warning on all my tires.