It's a really nice way to travel for families. We've used it several times, and despite the fact that I don't sleep amazingly well on them, the fact I can stash my kid and not hear a word about being tired and bored until the next day is really amazing. And then you get breakfast, and sit in pyjamas, watching the landscape as the train takes a smooth ride to your final destination. It's just a nice way to start your day.

Sadly the German Railways cut them out a couple years ago. As mentioned in the article, they were replaced by the Austrian trains (and also Hungarian), but the options became more and more complicated, at least for me (e.g. instead of boarding in Germany, go to Prague, and then board at 2AM).