all of those my personal ideas. others may think counterside.
it needs more time to be well enough. pieces are so seperated. Something is wrong with rightward areas. You should try Web2.0 styles or some other good color styles. your choice of blue and orange are not fit in this mockup. banner is so solid. it needs some more "things" in it. Leftward blocks’ headers is not good. needs some touch too.
next time you should use some stock photos or icons to make it more beautiful.
Solid white color is not well, i think. maybe a repeated background works fine.
These are my common points in design. i wish you good days.
I think the rounded corners in the nav area could use a smoother look. They are kind of a tweener right now between a straight cut and a rounded corner. It’s also a little strange how the top content box has an orange-box header without an outline, but the ones below do have one and are wider than the content area. I would stick with either/or and be consistent.