Has anyone went across europe on just night trains?

I don't know of anyone that has specifically done this over a full month period. I have used the trains for a couple of days - most recently about three weeks ago. We took the night train from Bologna to Munich and spent a day at Oktoberfest. That night we took the night train back to Rome and spent a day there before returning home at the end of the day.

Personally, I don't have any problem sleeping on the trains and there are places to get showers in some stations. As Brian pointed out, the sleeper cars generally provide showers (and breakfast), but will be quite expensive.

It is certainly possible, but you would be cutting your stays in each city to just a day if you didn't want to also stay in an inn or hotel or hostel once you arrive. I always schedule several overnight trains into my trips around Europe. I love being lulled to sleep by the gentle sway of the carriage and the clickety-clack of the wheels on the rails. Waking up refreshed a country or two later is such fun. The only time I ever had an uncomfortable overnighter was when we left Bologna bound for Munich. The train jolted a lot as it climbed the Alps.

I paid my "couchette" dues long ago when I first started backpacking and Eurailing, and always take a sleeper now. The berths are wider and more comfortable, the wagons almost always have a shower (I've had some hotel train compartments with a shower and bathroom in the compartment), there are fewer other travelers, if any, in the compartment with you, and all the younger travelers who want to party half the night are back in the second-class couchettes. It may seem a little elitist, but when you disembark the next morning, you can instantly tell who had a better night's sleep! Overnighting from city to city is not difficult and will be lots of fun for you. Give it a try, but be sure to allow a few days in each city.

I would love to do that but how can you sleep on trains? I find it so difficult to do so. But you are right it would be really nice. where would you start? and end?