A friend's daughter has an award winning blog on weddings and wedding planning. Wickedly fun and funny. She has been approached by commercial ventures about featuring their products on her blog for $$$. So far she has declined these proposals.
Nothing illegal about this practice, although the Federal Trade Commission is supposedly looking into it. I suppose the point is one of expectations. We have gotten used to branded uniforms on high school basketball players and NASCAR drivers dressed as walking billboards. The public is sophisticated enough to know that there is no implied endorsement. For better or worse, we are still somewhat in the infancy of the internet and I think the public has different expectations for this medium. Lest it not be obvious, the observations here are solely those of the authors.