(Sorry, I don't know how to mark this as a spoiler - anyone?)
On easy, I got stuck on the jump right before the pink powerup (run, I think). I seemed to fall well short of the next cloud.
On medium, I basically died when I moved in either direction - right or left. To the right, there is a flower that immediately killed me. And to the left, is a spikey brown toast guy that I can't jump over.