I'll be honest and tell you that I have no idea if Twitter is worth $8 billion -- the current value assigned to the company after the latest round of investment, which saw Digital Sky Technologies and others pour another $800 million into the microblogging service, according to AllThingsDigital. But I can tell you that the increase in Twitter's valuation over the last two years actually correlates pretty well with the increase in the total number of users and the expanding volume of traffic they produce, globally.

The same qualities that make social media an attractive ad platform recommend it as a communications channel to reach the general public during public health emergencies, according to an article in the New England Journal of Medicine by Dr. Raina M. Merchant, an emergency physician and assistant professor at the University of Pennsylvania's Pearlman School of Medicine.