I agree with John, whether or not one wishes to split scientific hairs in "labeling", the fact remains that internet addiction (a misnomer that should be called an "impulse disorder") has all the criterion to render it a certifiable disorder that would therpeutically be treated in accordance to standard practices of any impulse disorder. The prevailing criteron for any "addiction" is IF the cathexsis is powerful enough to produce problems within ones family, social, work, or recreational activities, then we got ourselves a bit of a problem here.
Utilizing this criteron, obviously if one uses the net for purposes of work, they are not an "addict" (excluding the possibility they may be on the net working for 140 hours/wk and might be a "workalcholic" (smile).
It is widely known that the internet HAS produced familial discordance and loss of social/work functionality. Families have been torn apart, marriages ruined, jobs lost, money squandered, etc ..all in the pursuit of an illusive dream externally while trying to amleiorate some internal "negative feeling". I think it is a serious disorder and should be recognized as such.