I just returned from a crossing aboard Cunard's Queen Mary 2, Southampton, UK, to Brooklyn. I recommend this ship on transatlantic crossings for singles. There's so much to do and a much more sophisticated ship experience. See my article on my crossing on CruiseMates' home page.
I'd guess that at least 25% of the passengers are single on transatlantic crossings. It's so easy to meet someone and I know travel agents have been getting terrific low single supplements, especially in the spring and fall. A friend is sailing in late may for a $300 single occupancy rate.