The in-built WordPress custom fields functionality is awesome, but it's merely a one dimensional string of text. There is a plugin called Advanced Custom Fields which some of you might know is a free plugin that offers advanced ways of having custom input fields (using the custom fields core API functionality). http://www.advancedcustomfields.com/
It's reached the point where I and my WordPress developing friends install this plugin first thing after installing WordPress. Either merging this plugin or something custom along similar lines would be great.