Put yourself in the engineer's place. What if you made a high-profile mistake and people who had never met you began to make inferences about your character from your Internet presence? Their conclusions could affect your career and even your love life. This worst-case scenario gives people--not just executives and entrepreneurs--a reason to think twice about how everything they make public might look to a stranger. What do you do about it?
Option one: Alarmists will try to erase all traces of themselves. I'm a huge meetup.com user, and we have a few people coming to our events who refuse to join the group or provide an email address; they just watch the website and show up at the same time we do. I'm personally offended by their lack of trust in me, and furthermore it makes me distrust them. In any case, if you don't manage your online presence, someone will do it for you. If all your next potential employer can find about you is your buddy's hilarious picture of you in a pink tutu throwing up in the bushes in 1995, then, well, that's your online presence.It would probably help to think about your life and your interests and look for gaps in what's presented online about you. Maybe your Internet presence is all work and no play. Put up some of your photography or poetry, or join a forum to discuss your car restoration projects. Paint a picture of yourself - selectively of course. You're cultivating an image, not fertilizing it!
Option two: To go too far in the other direction is also a mistake. Lifeblogging, the practice of putting it all out there, does serve to give a complete and accurate picture of a person. Anything really bad done by a person of typical morality would be lost in the tide of mundanities. But the problem isn't what's out there, it's the sheer absence of filters. Would you hire someone who didn't know when to shut up?
Option three: Ask what's reasonable and what's humanizing. There will be always be someone who will dislike you without giving you a chance - maybe because you eat fast food or drive a big car - so you can't please everyone. You make compromises based on your preferences, and as long as what you do is understandable in context, it serves to help an anonymous viewer understand you.