Cool idea to use the banana in such a way. Let's you design a lot of creative puzzles. What about having multiple bananas (but smaller?) later in the game? This could open up even more possibilities.
After playing a while, I ended up in a place where I needed to defend against a flying enemy, place the banana for a higher/wider jump, AND avoid having metal balls hit me from above ... oh well, that was it right there =)
Really like the art, physics and polish of it. Enjoyed it quite a bit!