We ended up choosing Disney Cruise Lines for our Anniversary trip this month. It might not have been my first choice but it was a function of trying to find a (nice) cruise that wouldn't be gone for more than 5 days, the week of our anniversary.
It might seem a little off to take a Disney Cruise, without kids. We've taken our little ones on this particular boat once before and we had a great time together as a family. But, we also noticed the adult-only sections of the boat were mostly vacated.
This trip, they weren't vacated completely but certainly we had no problems finding a spot on some cozy deck chairs, seats in the hot tubs or lounge space in the adult-only pool. We avoided the main-dining rotation, which is frantic with families and opted for the adult exclusive (and considerably nicer) Palo and Remy dining areas and off-peak-time buffets.
All said, it was a great trip, where Disney Cruise Line was concerned. The Veranda on the room was peaceful and the service was what you come to expect from Disney. While we probably won't ever get to do it again, at least not until the kids move off - I'd certainly recommend it for an unlikely adult-getaway.