We traveled Budapest to Amsterdam on August 6-22, 2013 on the Sky. It was a wonderful trip hosted by a wonderful friendly crew. It was a little hot in Budapest and Vienna but Viking was ready with plenty of bottle water on departure and cold towels and smoothies on our return. Viking seemed to be always prepared with contingencies.
One point many Grand European Cruise travelers fail to report is how much Viking is controlled by the river and acts of God. There was not much margin on many places along our journey. You could only look at the buildings at the ports and see the river gauges to see how the mood of the river changes. Only a foot rise on the Main and upper Danube makes river travel impossible. Some places we had one foot clearence between the ships railings and the bridge bottom. Most flooding is historically in June different from American Rivers. In cologne we had barges running aground on sandbars.
All in all a wonderful journey. Love the smaller boat. The only negative was the double docking with the Viking Frei covered our window in some ports we we to them in others. Oh well seasoned travelers are flexible travelers.