..is varied to say the least.  This fabulous infographic from @Meltwater shows just how much the role involves.   

For me, you could definitely add IT to this list.  Whilst not being an expert, not only do you need to keep on top of what's happening across the ever changing social platforms, you should have at a basic understanding of the algorithms used in order to optimise what you do.  Some SM Managers I know have also added coding to their many talents.

At Tribal Impact, coaching is another skill we use, working with time-poor Execs who want to improve their personal branding and build their networks.