The Pew Internet & American Life Project has just released a report and
a commentary about the internet’s role in the 2004 election. The report
is based on a post-election survey and documents how and why the
internet became an essential part of American politics in 2004. 75
million Americans – 37% of the adult population and 61% of online
Americans – used the internet to get political news and information,
discuss candidates and debate issues in emails, or participate directly
in the political process by volunteering or giving contributions to
candidates.

Report downloadable from here. Commentary by Michael Cornfield available here. His summary is:

The Project report confirms that the internet has become an essential medium of American politics. It has done so gradually, like other media. Yet, the internet’s distinctive role in politics has arisen because it can be used in multiple ways. Part deliberative town square, part raucous debating society, part research library, part instant news source, and part political comedy club, the internet connects voters to a wealth of content and commentary about politics. At the same time, campaigners learned a great deal about how to use the internet to attract and aggregate viewers, donors, message forwarders, volunteers, and voters during the 2003-2004 election cycle.