Superfish Menu in 2 Columns
Just about the time you posted your question, the new Superfish features showed up in beta.  These features include a multi-column capability. You would want to use CSS to style it, but the multi-column capability comes through the configuration panel.

There is a nice tutorial here:
http://www.digett.com/blog/02/19/2013/superfish-mega-menus

Pay special attention to the limitation: the multi-column nature of the menu is enabled for the entire menu, and you have to explicitly indicate any menu items that are to be excluded.

Presently, the dev version is the most highly recommended by the developer, but leave yourself a way to back out, in case you hit a problem.  

Also, pay close attention to the instructions for upgrading to v1.9

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