Pauline Draper-Watts has an excellent article at the Institute for Public Relations about the continuing dearth of measurement in the digital marketing arena. Although companies are increasingly dedicating larger and larger portions of their overall marketing and advertising spend on digital channels, firms are finding that an inability to effectively measure digital efforts provides a roadblock to effective digital marketing.
Draper-Watts notes that although "analytics tools abound for various social channels and owned properties with supporting metrics for those channels," since digital marketing is still relatively new, many firms are unsure about which key performance indicators are most indicative of digital marketing success. She argues that whatever metrics are used, it's important for those metrics to be clearly tied to the marketing objectives.
Good advice!