Best advice I got as a new mom (and after 2 little ones so far, know that they were always right)--"It's just a phase!" I often wish I hadn't fretted so much about our son's eating. He always stayed on the same line on the growth charts, although I was positive he was starving some months :) He is 3 now and still is not a good eater, but is plenty healthy! Unless your son goes down on the charts, don't fret!
My dr. had 4 kids in 6 years, so he's seen everything under the sun and was never worried about my son's eating habits. He said you'd be suprised at how little it really takes for a child to get the calories they need for growth.
I wish I somehow could've taken all that advice to heart better--we spent so much time fretting, being REALLY frustrated, worrying.... until he was about 2 1/2. I wish I hadn't wasted all that energy! :)