Just this morning found out about a couple of plugins that went under my radar until now:

http://plugins.elliotcondon.com/custom-field-matrix/
http://plugins.elliotcondon.com/advanced-custom-fields/

Looks like everything is powered by Custom Post Types in the advanced custom fields, and there’s lots of UI inspiration from some EE add-ons, but needless to say, something to take a look at.