In the April-June issue of Political Communication Eric Uslaner analyses two surveys of Internet users' behavior and attitudes to challenge the arguments advanced by Putnam and others that the Internet is accelerating the erosion of American social capital begun by television. Uslaner finds that people who are more trusting of other people are if anything slightly more likely to use the Net than those who are less trusting. But starting to use the Internet makes people neither more nor less trusting. As Uslaner points out, this makes sense when we remember that trust in this context means a positive relationship between people who do not have much in common with each other. The Internet tends to make it easier to find others with whom we have something in common, and communities tend to grow up around those commonly shared characteristics to the exclusion of "strangers". This chimes in with a discussion I had at my department's open day on Saturday with a student who is studying the possibilities of online communication between different ethnic groups living in the same locality.
Uslaner, Eric M., 2004. Trust, Civic Engagement, and the Internet. Political Communication Vol. 21 No. 2 April-June 2004, pp. 223-242.

