I conveniently avoided most parental problems by joining the Barrow Downs three days before my 18th birthday. I had not spent much time online prior to that. Now I am a part of email lists, post regularly here, have sampled other forums, surf using Google, and instant message with YIM, all on a daily basis. (And that's in addition to burying myself in Word for hours on end, writing fiction.) The 'Downs was my first real internet addiction, and therefore the one most logically to blame for all following ones.
If you kiddies want to scare your parents, tell them that Tolkien can lead to a life of staying on the computer till 6 in the morning, rather than out partying till 6!
Oh wait, I'm the only one who is scared by that....
To be serious, I suspect the most postive aspect of the 'Downs from a parental perspective would be the communicative and debating skills. You don't need the internet to become proficient in writing skills such as grammar and spelling, but to be able to put these skills to such regular use is invaluable. Forums in general, and high standard forums such as the BD in particular, present a great challenge to express, explain, and debate opinions and ideas. Daily exercise.
I only scored 15.77909% on that Geek test, incidentally. In my opinion it was too computer and Sci Fi based. I am sure I'd score much higher on a more literature/fantasy based geek test.