Influencers

I was in the shower this morning and was thinking about my day ahead (as I do) and get my brain 'in gear'.
I began thinking about influence and those that provided it.
Note:
I've just added the following to my Amazon 'wish list':
http://www.amazon.co.uk/New-Influencers-Marketers-Guide-social/dp/1884956653

This then got me onto thinking about the different types of influence. Perhaps it can just be as simple as:
Positive (of benefit to a company)
Negative (of detriment to a company)

Although hype, campaign penetration, brand loyalty, revenue and long-term market stability are all inter-related, perhaps these (or others) could be separate indicators of the influence individuals (or other entities) have on an organisation?