Don't forget to add "active" state of main navigation. As now you cannot see what is active in navigation
I would take away the white. It just doesn't look good. try a different shade of green I would say. Overall layout is pretty nice but maybe jazz up the articles at the bottom of the homepage. They don't really make me want to read them!
The template and layout looks simple but it attractive and color schemes are very pleasant to eyes.Personaly i like the header image and contents are well organised.
Theam of green color is looking very nice .... just think about ads place ads in footer also to get more adsense revenue