My two cents: depends really on where to draw the line on addiction, either: 1) doing something to the point of self harm. 2) doing something for far too long, to the exclusion of other, more meaningful activities.
I think it's pretty hard to say internet is an addiction like herion or alcohol - it simply doesn't have the same scale of health risks.... I mean the DT's can kill, as can heroin withdrawal. That said, there are plenty plenty plenty of examples of 2) people wasting hours and hours on nothing in particular online..... which reminds me, shouldn't I be working!!!
Joel