At more request, I've implemented a new function to the glowing mushroom checkpoints: saving!
Now, in addition to being able to reset to them when using the "Checkpoint" button on your in-game menu, they serve as save points! Exiting the level or the game and coming back allows you to continue from where you left off, instead of starting the level over entirely.
You can also reset each level's checkpoint in the main menu screen, under "Options".
Please drop a note in the Discussion forums if anyone has issues!
Patrick