It seems extraordinary Ed when you weigh up all these obvious pitfalls why LDLines strode forward with this idea in Dover. As you say, nobody has ever made it pay here. Greater distances are required. I believe the Irish crossing from Holyhead has the larger HSS things but I havent seen them, not having ventured over that way for a number of years. But on a crossing like that, or the one Marek mentions, they might be good as they could shave serious time off journeys that are too long. Speed would be a useful asset in those cases...too long onboard equals bored passengers.
Fortunately though, from a personal point of view, we had our brief stay in Boulogne in the summer, travelling both ways on the Norman Arrow. One of the spectacular things I remember about it...was summer evening, return journey, standing on the rear open deck/platform and watching the huge spray/wash being chucked up behind. Quite spectacular when the sea is blue, the sky is blue, and the wash is pure white snow..with added rainbows.
Colette has a few pictures of this...will see if I can get her to concentrate long enough to send them over..or even put them up herself!!
