I think as long as you slam something if you say "In my opinion" you are more protected by the First Amendment Right to free speech.  When you present something as a fact that is critical of a company or person that is when the gray zone of slander starts to emerge.  And often the person or company being slammed or criticized or slandered, has to "prove" damages to have a valid claim.  The law in this area is gray and somewhat subject to the whims and twists of lawyers, judges, regional differences and juries.

For example if I say "I think XYZ formula is a bad product."  I have a better defense than if I say, "The formula that company XYZ makes is bad."  The former is clearly MY opinion, the later can be construed as a statement of fact when it really is my opinion.

Jon Ahrendsen MD FAAFP
Clarion, Iowa 50525