I just read Will the Last Computer Hobbyist Please Turn Out the Lights? by John C. Dvorak.
Hello, John! What about LAN gamers, Linux users, robot hobbyists, arcade game enthusiasts, and hobbyist programmers?
Admittedly the plumage and behavior of your North American Hobbyist has changed. Consider that programming bar is much higher, so such programmers end up being contributors to OpenSource projects. Also, the computer field is less concentrated and much bigger compared to the era that Dvorak references. User groups now flock around a technology instead of a specific computer.
Maybe it's that the average computer hobbyist is now obscured because computers are now everywhere, and thus we no longer consider them hobbyists. They now are programmers, admins, etc...
Though I wouldn't doubt that due to the variety of modern past times that there has been a decrease in the tried and true hobbyist, for all hobbyist fields. Just look at the increase of discretionary interests: PC gaming, platform gaming, home theatre. In some ways everybody is a hobbyist these days.
And me? Well, I think I will paraphrase my sister on this, "You make your hobbies into jobs and your jobs into hobbies".