Sites recommending these sort of things - to read their children's diary and snoop on their web browsing habbits, for example - cause otherwise wall meaning parents to betray their children's trust, and in their attempt to get closer, they distance themselves from the child.
I'm 17 and in high school, and I see so many of my friends fighting with parents who don't trust them at all. These parents already act like this site describes, but an official looking web site like this is sure to reinforce the belief that a child, even one in high school, needs to be constantly monitored. In fact, they don't. Most kids, contrary to popular belief, are smart enough to figure out that if their parents freak out when they write objectionable content in their diary, the diary is being read, and they won't use it anymore. Likewise, they'll get a hushmail account, and the parents won't read the email anymore.
Most importantly, though, is that a good parent-child relationship involves trust. If there isn't any trust created by normal social means, then trust can't be forced by a parent. At best, they'll get obedience and possibly false information.
I know that I'm preaching to the choir here, and that it's turning into a rant, but I'm absolutely disgusted by the kind of garbage that's on this page. I've seen a lot of kids really screwed up by this sort of parent behavior. I know they'll have to deal with it for the rest of their lives, and here this site is, presumably trying to make a buck selling 'advice.'
My solution? As a parent, act toward you child as you would want them to act towards you. That doesn't mean you should let them run out of control and play with highway flares in the living room, but realize that they're human, and deserve as much respect as you would give any professional colleague at work. They're family, so it's reasonable to expect that they be friendly, but the important thing to remember is that nothing can be forced. As the parent, you have absolute power, and if you get upset about something, that can be very frightening for a child, even if they don't admit it. They just won't talk with you about that subject again.