i don't think it is a bad idea to move giambi to DH, he can hit and it gives one of the younger players a chance to get some playing time.
The biggest thing will be the fact that his abhorrent fielding ability is no longer a liability. Say what you want about Mientkeiwicz's hitting, but he's a Gold Glove first baseman.
Still, I wish they'd ditch the Phillips/Phelps platoon and sign Bernie.