Samizdata - 10:28 pm on Jul 6, 2010 (gmt 0)
I am not a lawyer, and you won't get legal advice on WebmasterWorld.
Laws vary from country to country (or state to state) - in some places it is actually illegal to insult certain people or things (rulers, flags etc) and saying they suck could potentially land you in jail.
In most of what is amusingly referred to as "the free world" you are generally entitled to hold an opinion about a product and to express it, as long as it contains no falsehoods.
Laws on defamation often apply to statements about people, with slander being the term for spoken words and libel the term for written ones. The case you describe would probably fall under the heading of "product disparagement".
In some US states there are special laws about food products, where opinions must be "based on reasonable and reliable scientific inquiry, facts, or data".
A Cease and Desist letter is essentially a threat of further action and yours will presumably detail what action may be taken if you do not comply.
It may be just an attempt to bully you ("chilling effect") or it may be that you have published something that could prove very costly in the long run - you have the choice to fight or fold, and need to consider what either is worth to you and how sure you are of your ground.
Everything depends on everything else.
If in doubt you really should seek qualified legal advice.
Hope this helps.