My wife booked it for my 50th last year (January). She managed to keep it a suprise until just before we got on the boat and 6 of our friends met us there.
It was a blast! The pontoon boat was decorated with "Happy Birthday banners and baloons and was set up with snacks and soft drinks as well as a to die for cake prepared by the YBC. It was a "chocolate lovers cake" with double chocolate and decorated with a large chocolate Conch shell and chocolate sea shells all around. Without question, the best cake I ever had and we still talk about it over a year later!
After we did a spin around the lagoon and a bunch of folks on the Boardwalk yelled out "Happy Birthday Boat Person" to us. It is expensive but worth it.
If you book, ask for "Captain Scott" he is great and kept us in stitches the whole time., We sailed with him again in April (no Birthday this time).
Once you've seen Illuminations this way it will never be the same.