A recent poll by the nonprofit Pew Internet and American Life Project discovered that one in five Americans do not go online, and have no plans to ever do so. And while there's still plenty of folks who are signing up for internet access, about the same amount of people are actually dropping their current access.
Some of the main reasons for avoiding going online included credit card info theft risks, pornography, as well as the high cost of computers and internet access. Believe it or not, literacy could be an issue as well, with almost one quarter of our population unable to read well. Wow.
Personally if you ask me - I think the number one reason for avoiding the web is right here. But that's just me.