Vote Intelligently:
Old/New Comparison! http://i.imgur.com/ldIrk.jpg
Moon Phases! http://i.imgur.com/2iFRw.png

I voted square, for these reasons:
1:You can totally do phases with a square moon.
2:Think of the implications of the shape of the moon (particularly its phases) - round-edged phases mean that something _round_ is blocking out the sunlight hitting the moon.
3:And, of course, tradition.

However, I do agree that:
1:Moon phases are cool, and
2:The new lighter blue shading around the moon is much-needed.
And thus I'd suggest that both be added whether the moon remains square or stays round.

If round wins out: The sun should be around 1.5x the size of the moon in the sky and have a larger and brighter corona (the outer brightness; see http://bit.ly/qRPl6X for what I mean).