Before I started posting (more or less) regularly in 2009, I wrote down three things that I thought should guide me in what and how I wrote. The first of these, "Link out before expecting anyone to link in (to my writing)", is central to how I think about the blog.
Whether or not I agree with someone else's work, I provide links to the original sources (unless they are not available, as is the case with paywall coverage). That approach gives any reader complete access to the same material I draw upon for my posts.
Over time, I've also come to follow a recommendation by Porter Anderson to "name-check" the writers, reporters and journalists whose work I am citing. I didn't do this consistently when I first started posting, but I think it respects the original work. It also makes site search more robust.
At GigaOm, Mathew Ingram rightly points out that a commitment to providing links is a critical part of web culture. Building on a story broken by Instagram's Marco Arment, Ingram reports that a fairly significant number of news sites and blogs skimp on providing attribution, let alone links to the source.
Ad-driven web sites feel a good deal of pressure to keep readers in a closed environment that drives up page views. On the web, that's the starting gate for a downward spiral. Posting for the sake of traffic undermines a site's credibility and value.