Network Neutrality

This post by Matt Stoller argues in favor of Obama over Clinton because of their relative stances on media issues, particularly Obama's support of net neutrality. Which is great and all, except that I have no idea what it really means. OK, it means that broadband providers can't discriminate against different types or sources of data passing through their network. But what are the practical implications of that? Who exactly would be affected and how? Why is that important? The Wikipedia entry seems to be written for people who already understand what it is. Can someone out there help me on this?