Background picture: You can use ResEdit to change the background picture yourself. It would be great to have a Preference setting for this, though.
Crazy comets: The comets are just a series of frames in a resource -- you could change that in ResEdit too. Again, it would be great to be able to just turn them off in Preferences.
Saved puzzles: It seems you should be able to save more (unlimited?) puzzles that have been started and saved.
Zoooooom in: The zoom mode is essential for some puzzles, but can make some users carsick. It would be more user-friendly to have a zoom window just around the cursor -- instead of the whole screen. On Windows, "BrainBuster" does this... you turn on magnification and there's a magnifying glass window around your hand cursor.
Multi-levels zoom: Along the same lines... instead of just "zoom or not", it would be helpful to allow multiple levels of zoom.
Kid friendly option: Having a preference that would lay down the shapes of the puzzle pieces onto the unfinished background would help younger children get more out of the game. Note that the "don't rotate my pieces" option is a great feature you have in here for kids, though!
Bravo... great program... hope you make a few improvements for v 1.1