Yes, as a young student in the late 80's... when the concept of air conditioning wasn't quite as widespread in Europe.

My memories include overcrowded and late trains jammed with backpackers (being alone with strangers in a compartment for 6 people in those old Italian trains could be somewhat stressful), noisy families on the boat, unwarranted concerns about my luggage's safety (had a friend whose car was tailed from the ferry's exit to Athens, and then stolen), a chaotic boarding scene for the ferry, and yes, getting seasick .

Note that I would have done it again, but with better planning and more intermediate stops, and not in the summer. The key, as mentioned by stimpy, is that I would rather spend 2 more days in Greece than aboard trains and boats, and visit Italy separately.

I am also quite fond of ferry crossings (once did Oita-Kobe hoping to board the nostalgic 'tatami class' old guide books talked about), but spending close to a day in normal class on these large Mediterranean ferries is all but restful: seating similar to coach on airlines in cabins the size of movie theaters, greasy snacks, and the constant auditory assault of the naturally loud denizens of that part of the world.