I am a big fan of rail travel in Europe and was planning on catching the train back to Vienna on my way home earlier this year, but someone mentioned the Meinfernbus as I was heading to the Westbahnhof, so checked it out. It was surprisingly cheap especially if you buy online (cost €9 for Graz-Vienna) and convenient. The time was roughly the same as by train. They are express services going from a couple of points in one city to a couple of points in another city. They are comfortable double decker buses with free Wifi.
If you needed to get to a smaller destination or ski resort you would still need train or regular bus but for intercity travel this looks a good option.