I have 153 nights on Regent Seven Seas in last seven years. Obviously, it is my favorite cruise line. Most of our friends that we cruise with are in our 40s and 50s although there are both older and younger. We did the transatlantic from Barcelona to Ft Lauderdale on the Seven Seas Voyager in 2004; it was a wonderful trip.
Seven Seas Mariner is my favorite ship. Although the cabins are slightly smaller than Voyager (and don't have separate tub and shower), I much prefer the public spaces.
I have some friends on the Voyager transatlantic in Nov 2011 but don't know anyone currently booked on Mariner. Both cruises are a terrific value when you realize that all food, liquour (except high end), excursions, port taxes, and even air are included in fare.
Please let me know if you have any specific questions.