Hoping James Lafferty can help here. I got fed up trying to change styling for the other Mail Chimp widget - yours seems more streamlined, and simpler.
However, how might I tweak the alignment so that the fields aren't right on the left edge (padding?). And can the submit button have some sort of roll-over code to make a hand appear instead of no change, or can it at least be highlighted in some way. Here's the page I've currently got it on - http://www.shospace.co.uk/blog
PS. I've made the change to the code to keep the form up when someone subscribes - I know you've said you don't like that, but to add another voice to your objectors(!), I prefer having the look of the site consistent, so it doesn't disappear.