We just did the Encounter in Freeport this past Tuesday (9-24). We (myself and my 6 y.o. son) liked it a lot.
Positives: The entire presentation was about an hour. The people were extremely knowledgable and informative. We spent at least 5 - 10 minutes on the platform in the water with the dolphins, petting them, etc. While we were waiting our turn, we spoke with the trainers, and were only about 10 feet away from the dolphins.
Negatives: 30 minute bus ride from ship to boat loading area, 30 minute wait for the boat, 25 minute boat ride to sanctuary, and then all over again to get back (we were told that the sanctuary used to be a lot closer, but they moved to a more remote area because of boaters and fishers polluting the waters). It was hot in the sun, but, hey, it's the Bahamas and we expected that, plus there is shaded areas you can go to if needed. They had a lot of rules (no eating, keep your hands in front of you while in the water until they say it's ok to pet them, etc), but none seemed out of line, and they said it can confuse the dolphins training... The picture they took wasn't great, but ok enough that I bought it...
We opted for Freeport rather then Nassau because the brochure said it was 3 hours vs. 7 hours. I suppose if the stars and planets all aligned it could be done in 3 hours, it was 4 and one-half hours for us (left the ship at 11am, got back right at 3:30pm for Island Magic).
We would have done the Dolphin Swim, but couldn't because of minimum age restrictions. It was expensive, but I thought it was an opportunity not to pass up (we don't have many dolphins swimming around here in Wisconsin). I don't think you'd kick yourself if you were on the fence and skipped it, but we liked it, except for the fact that it took a lot more time than expected.