The stats here may be a little outdated (noted in Sep 2009), but is nevertheless an interesting pointer. A study published by the MiniWatts group notes that the world now has one-fourth of its population online. Sounds interesting though I sceptical in that the internet penetration is not even 10% in countries such as India where a huge chunk of the population is.
North America : 74.2%
Australia/Oceania : 60.4%
Europe : 52%
Latin America/Caribbean : 30.5%
Middle East : 28.3%
Asia : 19.4%
Africa : 6.8%
World Average : 25.6%