We booked online and just claimed the actual paper tickets at the Minoan Lines ticket booths at the port in Piraeus (Athens).
We took the Mykonos Palace and the travel time was less than 7hrs.
Departure: 4pm
Arrival: 10:30pm
Overall, it was a very pleasant trip. We fell asleep as soon as we got settled in our cabin.
I was told that no videotaping is allowed inside. So I just tried to snap a few picsas quickly (and as discretely) as possible.