I'd lower the skin weight on the hips a bit; the bellybutton really doesn't deform well. That, or lower your bone structure around the hips to compensate a bit (it's hard to tell without seeing the rigging and geometry :) ).

The secondaries are also a bit limited; there is no rotation of the pelvis/hips at all, giving it a very mechanical look.
I'd suggest rotating the pelvis bone by about 10-15 degrees (depends on the type of walk you wanna achieve; your actual mileage may vary) and the shoulders slightly less, but in an opposite motion (when the left hip is forward, the right shoulder is forward). It's a normal manner of keeping balance for most bipedal creatures. This, in turn, will make the arms move inside and outside their line, into an arc instead, which will also improve the feeling that it's not a machine. :)

Another alternative to rotating the pelvis along the Z axis would be to rotate it along the X axis (if you take into account that the X axis goes from forward to back); this would make it look more like this:
http://www.youtube.com/watch?v=occFkFbl3ms

And one last bit of critique would be to make it a tad faster. Right now, it feels more like he's doing a gym exercise than actually walking.
Don't worry too much about that one; I made the exact same mistake in most of my early animations. ;)

Otherwise, that's off to a good start!

No problem!
I haven't animated in a while, but there are certain things that everyone does wrong at the beginning. Only fair to spread the knowledge. :)