Somewhat true, but people unknowingly put more of their personal info online than they think. Google your name, I bet in 15min you can find your screen name on here, and any other open forums you may be a part of. Most of us entered our legit name in the background, some forums require it to create a screen name.
Just saying that in some fields, online behavior can make or break you, even in narrow forums such as this. Disregarding the fact that we have random drug testing and a fail is immediate termination, I wouldn't fear losing my current job if I stated online that I did illegal drugs. I would, however, more than likely take myself out of running for the position I am trying to get at another job by the mere statement of such behavior.