Having said that, the only point I really want to touch on from the article (being that most of it has been said very well by others by now) is that I do not agree with the recommendation that people need to put 'my opinions are not those of my employer'.
I am myself as an individual first, and a represesentative of my employer second, not the other way around. It should not be the responsibility of a person to state who they are representing when they say something, but rather the responsibility of the company to make sure their spokesperson states they are speaking at that time as a representative of the company. If a person reads my statements as a de facto opinion of my employer, then they drew an incorrect conclusion and should have known better. If it isn't explicit, then don't assume.
Having said that.....making statements that are disparaging of one's employer, or reveals their internal business workings, should not be done lightly. It might not be illegal, but if you are an 'at-will' employee offending your employer with your antics could swiftly get you reprimanded or fired. A good acid test might be if the statement is not something you would want to say to your boss directly, then you may not want to say it and have it get back to them indirectly.
Freedom of speech is a two-way sword. It might be your right, but it's also your responsibility. You have merely the right to free speech, not the right to be immune from the fallout of your words. Both come as a package deal.