An update has been submitted to Apple for review. The update includes removal of the clicking noises sometimes heard when tones play back to back as well as the addition of new instruments piano and guitar. Just tap the square multiple times to make it show up in different color and play different sounds. Some minor bugs were also updated.
Future versions will include the ability to shake the iphone to clear the lit up blocks as well as some means of saving your creations to share with others.