Is sending an e-mail worth a penny to stop spam?

A plan by Yahoo to have its e-mail users voluntarily pay a penny for each e-mail they send to help cut down on spam may test the limits of how much -- if anything -- people are willing to pay for anything on the Internet that is already free.

Even the lowly penny may be too much too much for people to pay in an age when newspapers are trying to stop giving away their product online, and a book titled "Free" is a New York Times bestseller that promotes the free model as a smart business strategy.

People may be slowly agreeing to pay for more things online that used to be free, and micropayments are becoming a hot topic, but free speech associated with e-mail may just push it a little too far.