I recently had my first cruise with the Fred Olsen line from the UK having previously been a P & O cruiser. On the latter their dance areas are very small and they do not provide dance hosts for the benefit of single passengers.
On Fred Olsen I found the dance floor about twice the size,even for such a small ship ( about 850 passengers) and they had 1 lady & 3 gents hosts. Each evening at 7.30pm, after 1st sitting, the resident orchestra played ballroom music for 45 minutes before the first show after which there was a further 45 minutes dancing to records. I am 82 & still love ballroom dancing and find it keeps me very fit. Being able to dance with a good partner made the holiday so enjoyable for me as a widower & I have booked 2 cruises for 2015.I have created a CD of my favourite ballroom music in the hope that they will use it on my voyage to Tenerife in the New Year.

My wife and I sailed on the Crown Princess two years ago with one of the ballroom cruise providers. Although there was no provision made for private ballroom dancing per se, a subgroup of us "took over" one of the lounges in the evenings. There was a quintet playing there after dinner who played nothing but ballroom once they saw there was a group of serious dancers who appreciated and actually danced to ballroom music. The floor was rather small but adequate if you kept your traveling in check.

Unfortunately, so many passengers came down with norovirus that the cruise was cut short and we returned to Lauderdale 3 days early after sailing almost to South America with no stops. (See "Princess Noro-Cruise to Nowhere" on cruise boards.)

Princess did give us a full refund and paid our airfare home, but that was our last cruise. It's not worth the risk to us of having a pricey vacation ruined being trapped at sea while our fellow passengers are vomiting in the hallways. And in the elevators. It can happen on land too, but there you can at least crawl to the beach to die.

The saving grace of the cruise was the dancing. Although one instructor got sick and we didn't see her at all after the second day, the remaining instructor was outstanding and he made up for a lot of the hassle.

Your experience may vary, of course...