We can see the size of characters! I found this picture floating around the internet and decided to put it up. Bowser is bigger than Peach AND Mario AND Luigi, but Petey is even bigger. A Bullet Bill facing right is about the size of Mario, Lakitu is about the same size as Mario, Shy Guy is about the same height as Diddy Kong (who is the same size as Dixie Kong) and lots of other stuff.
Click on the picture for full size. Hmm...where did this picture come from? Nintendo Power?