Kate Kaye has a story on Clickz about how candidates are using e-mail and she reports its for more than just fund raising. From the article:

McCain and Giuliani use it to push their books, Clinton and Edwards to get personal, and Obama to get the netroots out on the streets. In the political world, as in the e-commerce world, e-mail is often considered a tool best suited for bringing in the bucks. However, political campaigns are not only employing it to promote fundraising, but to update supporters while on the campaign trail, target opponents, promote events, push paraphernalia, and even appeal to their sweet tooth.