No, one of the most formidable challenges facing Google is likely sitting in your pocket or purse. It's your cell phone  and it will put added pressure on Google and other Internet companies to revamp the way they handle online marketing.

As more people use cell phones and their tiny glass screens to gain access to the Internet, Google and its fellow online advertisers will have less space, or what's called "ad inventory," to place marketing messages for customers. Google makes money selling ad inventory. Its ad inventory is diminished on a cell phone.

iPhone as Tipping Point

Google can now fit about 10 ads on a standard computer screen. (If you look at Google search results on a PC monitor, paid ads are the listings at the very top and along the right.) However, on your cell phone, if you type in a search query at Google.com you get only one or two paid ads in response.

Imagine the horror that would befall your business  if a large slice of what you sell suddenly disappeared. A similar fate could befall companies that depend on online advertising, as small screens become the gateway to the Internet.

Of course, no one's suggesting that consumers will abandon standard computer screens overnight. Early research shows that mobile advertising may be more effective than standard online advertising, suggesting that it will be more lucrative for the companies that rely on it. Still, the shift is coming fast enough that Google must get prepared.