It seems once you leave the borders of the United States traveling by bus is a very common way to get around. In Mexico we used buses within towns and also to get from town to town. They are cheap and there are a lot of them. Though it can be a bit intimidating navigating the system at first, after a while it gets a lot easier.
The biggest challenge these buses have for the traveler is lack of luggage space. Rarely will you find an overhead shelf or coach style compartment. So if the bus is crowded that means you have to sit with your backpack in your lap.
The other big challenge is knowing your stop.