Looks pretty good, but I suggest you get rid of that blurry black shadow layer around the progress bar. It'll make things a lot easier if it's not there, and in my opinion, will probably look better.
I also think if you put this up with other themes, you should change 'iPod Name' to say Rockbox by default, but use the .wps to put it there so others can change it if they want. I'm not quite sure if you've used different fonts or not but keep in mind you can only use the Rockbox system font (10px schumacher, I think) and a font of your own choosing say 15px Lucidia Console (but only one size as they're bitmap fonts).
Someone with better knowledge can tell you for certain, but I'm pretty sure you won't be able to make the status bar green like you have in your mockup. If I recall correctly it's hard coded into rockbox and is a mono bitmap so even if you change that, you'd probably have to write the code for it to handle colour. Also there's currently no shutdown option on the main menu, unless you use a custom build...