I Based this page on hints and secrets and stuff or just things I guess the Programmers didnt want you to know, also the 2nd section has spoilers.

          ~Duplicator Made of Rock Structure~

 ~In the Mermalier - Marble Room - Start by going on the Switch that brings up the wooden board(or better, the brown metal platform), kill the robot by the tiki with a bubble cruise, notice a duplicator produce the same robot. If you use the bubble cruise to check down from where it came, you can go by one rock structure and hear the duplicator, I call it the Rock infused Duplicator. It's one of the rare duplicators that can't be defeated.

                ~ Secret Ball Areana ~

Beat the game, press b to skip the credits, it will take you to the center of bikini bottom and notice where you start is now an arisen platform, if you press R by it, you can enter the secret ball areana and get more shiney objects and just have fun(Note: You can only stay as ball sponge, you cant be the normal sponge bob in the ball room)

              ~The Invisible Boat Mobile~

Go to the Mermalier and go to the first bubble bowl bridge in the first area, as you cross it, look for a white display like platform with a tiki infront of it. Smask the tiki and a switch will be revealed. When you hit it, for a split 2 secs it will show then go invisible.....you can actually jump on it and stuff as if you were standign on thin air.~inn0cent06started by the Blue line is a spoiler.

                   ~Mysterious Mime~

When you beat the Robots in the 3rd part of Bikini Bottom, Go to the window to your right, you should see a mime.

                   ~What Water?~

At the castle of Goo Lagoon, when your at the entrance and u press the button to not only raise teh gate but to rise water, you will probably hear sponge bob say "Water!Rising! Must Get to top!"

If you go to the entrence area again, sponge bob will say it even if you dont press the button.

    ~The Annoying Bus you can't get on!~

Remember the episode Sponge Bob gets stuck at Rock Bottom and when he goes to get some candy, that darn bus leaves as he is about to order it? Well at Rock bottom if you go up to the machine, the bus will come and go!

                    ~Concept Art~

Go to the Theater labeled "Revenge of the Bride of Plankton's other Bride." Pay the of 40,000 Shiny Objects and you can see artwork of stuff in the game. 

                     ~Black Pit~

If you pass the taxi platform and go around the Rock Bottom entrence, you can actually jump down the Rock Bottom Pit ... and Die, I figured you could not even go that far. 

                    ~Duplicator of the Lake~

At Jelly Fish Feilds, go to the spot where you had to fight the robots that you daze and threw at the mini water pumps. If you go back you can here the duplicator, also if you did not do that mission, look at how the Ham-mers just magically jump from the lake on the ground your on.

                     ~Crimanal Profiles~

Inside the Police Station (Bikini Bottom part 2) is a Data Base on the robots.

                     ~Musical People~

When you hit someone like Squidwerd or Bubble Buddy w/ a Bubble Cruis (or any other weapon), you can hear a muscial noise or sound come out of them.

                    ~Mysterious Darkness~

Go to "SpongeBob's Dream" and go in Patrick's Dream. Here if you go all the way in one direction in the dark, you will come out from the opposite wall.

                   ~Changing the Channel~

Inside the Retirment Home, go by the TV and swing your bubble stick at it. The only channels are the default one and Jellyfish Feilds.