http://en.wikipedia.org/wiki/Internet_addiction_disorder
Internet addiction disorder (IAD) is now more commonly called problematic internet use (PIU)[1] or compulsive internet use (CIU).[2] Other overlapping terms include internet overuse, problematic computer use or pathological computer use – and even iDisorder.[3] These terms avoid the word addiction and are not limited to any single cause, but only reflect a general statement about excessive computer use that interferes with daily life.[4]
The jist of it is, that if you suffer from low dopamine reserves, the gentle and very subtle stimulation of dopamine is triggered constantly by using the internet. Constant feedback and results. Pleasure and reward principals.
So... if you find yourself spending too much time on the internet, a probably option for you is to take dopamine supplementation.
If you are a burn out, which no doubt the majority of people here are, try L-Tyrosine, or L-Dopa (Haven't tried the L-Dopa yet), or an anti-depressant... I am not a doctor...