Most people talk about the cost of spam as just the time spent hitting the "d" key. However, there are two much darker consequences. First, people change their online behavior to make themselves less accessible by e-mail. For example, just in the last week I got two requests from people to take their email addresses off articles posted to Advogato. Many people believe that the purpose of email and the Internet in general is to foster more open communications. Spam makes it less so. Second, overagressive spam filters sometimes cause serious difficulties. Here is one recent example: http://boingboing.net/2002_08_01_archive.html#85361424 Entities like SpamCop would not be necessary if it weren't for the volume of spam, and they certainly wouldn't be able to shut people's websites down.