If I have a blog that just talks about other websites in a good way, promoting I guess you can say, is it ok to use their logo?
I believe you be covered by fair use to a certain extent, just have some sort of way for someone to contact you to remove content.
If they do a press release, that includes the logo with permission to use it, then yes. But just doing a review will not be covered under fair use. It is just like using images of a product and writting a review of it using those images.
For the most part you can use other people's logos, depending on the source and the company. As Dreads said, make sure that you have ways for other parties to contact you listed on the website. It may not be technically legal, but unless you're getting a large stream of traffic, or are not a highly profitable business, most companies will ignore it. They're not going to take an individual to court every single time their image or logo is used. What they'll more than likely do if anything is email you and ask you to take the content down.