I remember hearing this is actually a developmental stage when they are learning about cause and effect, up and down, what happens if I drop this, how big a noise will it make when it hits the floor etc etc.

I would be somewhat tolerant of it but if it is all dropping and no eating I would call it quits for that meal.

Don't forget that their appetite starts decreasing in the second year because they aren't growing so quickly. DS used to eat WAY more as a baby than he did as a toddler. Also make sure that your DS isn't drinking too much milk and therefore just isn't as hungry for food because he is filling up on milk. I always used to try and get half of the meal into his mouth before offering a drink because even a small drink would take the edge off his appetite.