I was reminded of one of my pet social peeves as part of a conversation with one of the, astonishingly smart, Google interns. One of the most challenging aspects of social networks is that, broadly, people within companies don't really know what "doing a good job" looks like. Depending on the organisation, social media can be part of marketing, PR, customer service, a specialised department, even IT. The aim of these departments is often mis-matched with the potential or the audience the brand has across their social media, so it is difficult to create effective performance measures.
Most well managed teams create measurable goals - increase X number by Y percent and so on. However, when you chuck something as mutable as social systems into the balance it is difficult to avoid putting in numbers that qualify as vanity metrics, rather than useful data.
Vanity metrics is a term from the world of lean start-ups, and refers to numbers that people quote because it makes them feel good, rather than because they matter. An example might be numbers of links to a piece of software rather than number of customers, or the number of viewers of a page rather than number of signed up users. The idea is that there are certain key figures that reflect the business model underlying the startup, and measuring those is far more important (and often more difficult) than tracking numbers that are easier to measure (and make you feel better).
Something like circled/follower/fan count is a classic vanity metric - it will (in general) trend upwards with the growth of the network, and a lot of social teams are measured on their ability to increase this single number without any respect to what it actually represents. I've heard quite a few stories over the years of notable brands discovering that 50% of their "fans' don't know the brand has a page at all, or that that their followers are not in the demographic that the company is spending millions of pounds targeting.
That said, there is significant challenge in actually creating metrics that matter. Much like television advertising, there is value in exposure to a brand or product, and that certainly happens across social media, but is extremely difficult to measure. There is significant value to good customer service, but in general if you respond well to someone they just go away! On a network like Google+ where the default method of communication is to a limited circle of people, there may be no way for a company to tell that a user is promoting a brand with which they've had a good experience.
It's difficult to talk about social media - I've been on the side of a brands representing themselves (with Virgin), a user of a network (as myself!), and of a network provider (with Google), and it hasn't made it much clearer how to avoid this problem of focusing on numbers that are easy to measure but are of limited value. I am completely convinced that the best approach to any social system is to treat it as a series of conversations between people and to be human and honest in any communication, but I have yet to find an ambient measure that can be easily extracted to let anyone know how they're really doing.
Classic marketing metrics like net promoter score are still an excellent way of measuring engagement with a brand, but overall I think it's really important that companies keep experimenting and evaluating, and looking for the metrics that track with what makes a difference to them.