Nice and clean but extremelly frustrating font choice. Why user can customise body font but not headers, user's names etc.? Since you are using different fonts (including "Yanone Kaffeesatz" for crying out loud :( ) users with different languages installed will get a mess instead of frontpage with very strange font substitutions.
Please have a look on this.
Also color picker is next to useless due to limited amount of colored elements visible. One great way to showcase it will be having colored background strip for the logo changing color.