What I like best about sleeping on European trains, though, is the experience. Of course you could find yourself sharing a compartment with strangers who snore. If you can afford it, you'll want your own private compartment for two or four. Happiness is rattling through the night with friends or family that you actually want to rattle through the night with.
My last overnight train experience was from Sicily to Rome. Sure, I could have flown. Instead, my wife and I boarded a late evening train in Taormina. While we slept, the train was taken apart for the ferry ride across the Straits of Messina, then reassembled on the mainland. The next thing we knew, it was early morning and we were in Rome, ready to continue our adventure. I wouldn't have traded the memory for anything.
You can make all your plans through your travel agent or through Rail Europe at 800/438-7245 or www.raileurope.com.