on the first level you can double jump to the higher section of the gray cliff, then head to the left, across the waterfall and you can jump off and fall forever... there are tons of other OOBs its hilarious
By the way, have you set up a speedrun.com page for your game? If you havn't i think you should... then people could submit their scores and do different category extensions. (like, no targets speedrun or no rocket jumps))