I really like O'Reilly's simplified definition of Big Data and Introduction to the Big Data Landscape. Big Data is volume (how much data), velocity (how much new data, and how much does the data change), and variety (both structured and unstructured data). Big Data is "hot" because the technologies to solve Big Data challenges are more accessible - cloud, in memory databases, easy to use visualization tools, new database options (nosql, xml, ...), and choice between open source and commercial tools. Big Data is also Big Business, and is sized to $50 billion by 2017 with both big and small vendors competing. Also, new data and analytical capabilities has the potential to transform entire industries.
Big Data also presents both talent and organizational challenges, but more on that in another post.
In talking about Big Data with a colleague, I realized what should be important to the CIO today is that Big Data is relative. How much volume, velocity, or variety that "defines" Big Data is relative to the CIO's capabilities (both technical and organizational) versus the competition in the industry. So an organization that is lagging in Big Data and analytical capabilities is going to find that their competition is smarter, faster, and possibly more profitable. A CIO that can drive the organization's Big Data capabilities has the potential to create a strategic advantage versus competition.
Big Data is about scale - can the CIO outpace the organization's vision on what it wants to do with data using a combination of talent, technology and process? If the organization doesn't have a "data vision", then the CIO needs to paint the canvas of possibilities by demonstrating new analytical capabilities.
So yes, there's plenty of media and hype, but the CIO has to pay attention.