Advertisers pay to post details about their "opportunity," specifying, among other things, how they want bloggers to write about, say, a new shoe, if they want photos to be included, and whether they'll pay only for positive mentions. Bloggers who abide by the rules get paid; heavily trafficked blogs may command premium rates.
I just want to be clear, I do NOT do anything like this. I post about Pearl Jam, Superman Returns, books I read and OpenBSD because they're things that interest me. I am, in no way, compensated for anything posted here. I do get a very small percentage from the icons at the bottom of my page and the occasional Amazon link, but I imagine that the only payback I get from those are my own click throughs.
Superman Returns was an example given in one of the articles. Since I posted about Superman Returns, I wanted to make it clear I do not participate in such practices. That is all.