Now, obviously bus trips can be horrendously long (todays trip will be 14 hours), but I think they tell you so much more about a country than flying from one city to another. When I was in Israel last year, I took a bus from Tel Aviv to Haifa, which was not very long, but it showed me so much of the country and landscape which a quick flight at 30,000 feet could never do. We stopped off several times at gas stations to eat ice cream and buy snacks. It was a road trip, through and through.
And that's the best thing. Buses and trains afford you plenty of window time (and something to see), where the journey informs the experience. On an airplane, the journey is something I want to forget.
* I have very basic itineraries in each city, containing interesting areas to visit, along with specific buildings I want to see. But there is no schedule for when I will do what. So these moments of downtime let me develop a better understanding of where I am going. I essentially cram for the next city. I like to travel this way as I can let outside events alter the course of the trip as the unexpected things are usually the most exciting.