the flat boxy design is quite in at the moment – yea I like it. Personally I think I would add alter the BG colour of the content area to be a touch lighter, so you get a little more contrast to the box.
Like I said, the flat boxy idea is going well, but maybe you could add a little detail, maybe a gradient fill to your header BG, from like that nice dark blue, to a slightly lighter version of it, that kinda thing.
I think im basically saying, good design idea, nicely presented. Just needs some spit and polish :)