Word of mouth (or fingers...)
I fail to see how this is much different from bad-mouthing a company's products in the street, apart from the exposure level (but then again, just because you *have* a forum on the 'net does not mean that everyone will automatically visit it). Fact is, if you tell enough people how bad something is, sooner or later it will start to affect sales - the medium is irrelevant. Hell, if Microsoft decided to sue everyone who bad-mouthed Vista, it wouldn't know where to begin!
This would be the start of a worrying trend if 2clix won, and the fact that they're trying to smack a site down for airing public views and experiences about a product they sell should be reason enough to steer clear of them (hope I don't get El Reg in trouble for saying that!) ;) It's my hope that 2clix will discover the SCO effect - lawsuits tend to leave a bad taste in peoples' mouths.
What next? Sue any review site because they gave your product a bad rap? Where does it end? Will all Web sites be neutered to a point where criticism of any commercial product is forbidden?