I've done it, and encourage others to do it many times on this site - I'm starting to feel like the official mascot.
It was one of my favorite parts of my cruise, totally worth it. Something you won't see anywhere else. Look in my post history (or even at cruisereviews.com for the "Carnival Miracle" review by Mike) for a bit more detail. The only bad thing I can say about it is that the ride to get to bio bay is a bit long - over an hour if I remember correctly.
Not sure if RCCI has this trip, but I'm sure an independant company does (if you don't mind that sort of thing).
I too am interested in seeing the Bioluminescent Bay! But my ship does not dock until 3pm and then leaves at 10pm. Think there is enough time to do it? And if so, does anyone have a good private tour guide in mind? Royal Carb. does not list it under their excursions.
NCL Dream 10/2006;RCI Liberty of Seas 4/2008;Carnival Valor 10/2010;Carnival Freedom 11/2012 Read and post cruise reviews
Do a google search for Bioluminescent Bay and you will find a website for a tour operator. You will have to contact them and get a quote and tour schedule. But I would think that you would have to go late and most ships don't stay in port late enough to have it be dark. But you never know...