Yes, I cruised as a "truly single" last December. Just a regular cruise (not a "singles cruise"). I'm a 40-year-old divorced female. Booked a room just for myself and paid the high single supplement---but I also felt that was better than just finding anybody that would go with me, as I could come and go when I wanted, not worry about sharing the bathroom or the extremely sparse cubic feet of space in the cabin, snorers, smokers, people that felt they were obligated to "tag along" with me everywhere, etc. I called a travel agent and just booked the cruise. Told the travel agent that I wanted the LATE SEATING for dinner, as more families will book early seating, and the odds were better in late seating to have other singles. She asked what size dinner table I wanted to be seated at---I specified THE LARGEST, again upping my odds of meeting more singles, or even just more people. The travel agent, as well as other people, advised me to go to the dining room as soon as I boarded the ship and request to be put with other singles, although she said that most ships try to put people in "cabins for 1" together. I ended up at a table for 10---five of us were singles, and then there was a couple with their two children (who, I might add were wonderful--so many people snub families and children).
In addition to that, just get up and about, go everywhere and do everything---there WILL be singles around. It seems like everyone says Carnival is the line to take for singles, but I went on Royal Caribbean and had a fantastic time. Go to the lounges, discos, pool bars, etc--and there will be singles. On the ship, these are a lot more like "meeting places" than the typical lounges/bars around towns (which I do NOT frequent). I was rather worried before the cruise, as I tend to be a very shy, introverted person, but I just made a point of getting out there and enjoying myself....it is what you make it!
You should avoid the usual "spring break" and "school vacation/holiday" timeframes, as the ships tend to be predominantly "family oriented" at those times.
Having said all that, feel free to contact me if you have any questions. Do you have a cruise booked? What line and when? More and more people traveling as "singles" now than ever before! Have a wonderful time---you deserve it!