There are some great views expressed here. I'd comment only as far as thinking about organic social skills verses those that might be best for using social in a paid manner.
For organic social management the focus is on writing ability, passion for the brand and industry segment knowledge since many times you will want someone who can comment on things outside the brand per se but that are of interest to your community. You need someone who's passion for this will last over the long term too, so you establish credibility and engagement within your social community over time.
For paid social programs, understanding business impact, ROI and data analysis skills becomes far more important because the ability to build different audiences, run paid programs and find sweet spots of performance is a very data driven process and tends to be less creative.
Our experience is its a very tough job to get creative thinkers who write who also have a passion for data, statistics and business performance (good luck!)