One of the drawbacks I feel in WordPress (Free Edition) is in the limited number of themes, and that usually drives some people away.
Why not consider having a theme sharing platform for WP Users? The main idea is: People can just browse through user-uploaded content (which, maybe, has to go through some sort of WordPress QC) and then apply it for use in blogs everywhere in WP (.com/.org applicable)
To detractors: I know there's one right here at http://wordpress.org/extend/themes/, but it only allows users to download approved WP themes. But the main difference in my idea is a platform for people to get more themes, that people who don't pay can use.