A couple of days ago I referred to another blogger's post. It indicates that our client's transferrables include their social networks. Today I learned that there's some hard evidence, on the Barking Up the Wrong Tree blog. See Should prospective employees be judged by the size of their networks? where an MIT report says that each IBM employee's "e-mail contact was worth an added $948 in revenue" on average.
Of course not every prospective employer can be expected to know and understand the value of a network.