When reviewing things, this should be provided. For example, Zaine Ridling is quite passionate about XYplorer or Opera, but we know he is simply a happy buyer, and he's not affiliated with the companies providing them. Another example are the people working at Ars Technica, which reviews devices that they use, and they're quite honest about them (except those reviewing Apple products, the iPhone review is a perfect example of this). Or Coding Horror. An example of how it should not be done it's WinSupersite, as nobody can believe this guy is talking honestly, or sometimes, Scobleizer (although I must admit that I've been out of touch with his blog for some months now). That's what these bloggers were talking about.
A political blog is not an adequate example as it's practically impossible to find someone really independent. In your case (USA) you have, for example, the Daily Kos and Michelle Malkin's blog (not quite sure about this one, so feel free to correct me) and we all know they are not exactly independent, but terribly biased towards one or another party, so biased it almost makes me wanna puke. Besides, we know that republicans and democrats are the same dog with different necklace...
*mouser bans Lashiec for talking about politics in the forum*