Internet procrastination can have multiple causes, which aligned with each other provide the disastrous results.

• random reinforcement schedule -- I have found also many valuable things online; the problem is I get them randomly

• social activity superstimulus -- internet is to human interaction like sugar is to food

• trivial inconveniences -- clicking another link in browser is easier than standing up and doing something else

• instant feedback loop -- loading a webpage takes a second on average, many our activities are a few magnitudes of order slower

...and this is just for websites not optimized for being addictive. For example blogs are more addictive, because their timeline creates a sense of urgency. Blog comments create a lot of noise attached to the interesting content. Wikis contain too many links.