I have done this twice now and I will be going back for more in 2012. You get a great behind the scenes of the Living Seas and a awesome trip into the big tank. The best part may be playing with the children that are watching you. So much fun from both sides of the glass.
though your only in the water for 30 minutes, it's one of the best tours I have ever done. look forward to redoing the tour each time I go back It's not so much the dive that make sit fun, but the way the Guests at disney interact with you through the glass that really makes it exciting, to see the look on little kids faces when your playing with them or showing attention to them while your swimming. I can't wait for my 3rd, 4th or even 100th dive when I am there.