Negative reviews are kind of a touchy subject. Bloggers often get criticized for only posting positive reviews or talking about products they enjoy, despite many readers expressing interest in hearing about the less than impressive products as well.
For me, I certainly prefer writing positive reviews, simply because it's much more fun spreading the love than sharing disappointment; however, as an avid blog reader, I also understand the need for negative reviews, as they can often help guide one's purchases.
The way I decide whether or not I'm going to crunch out a negative review or mention in a post is to consider whether or not there's a lot of hype surrounding the product. If there is, I will likely talk about it because, chances are, people are interested in reading about it, one way or another. If it's a product that is lesser known or flying under the radar anyway, I'll usually just let it go, as I figure there's probably a reason not many people are talking about it.
I'm curious what your thoughts are on negative reviews. Do you like to write them? Read them?