Talking to people online. Reading, keeping current, increasing your knowledge. Working on hobby projects. Enjoying a good book. Writing for your blog. Tweeting and (more often) reading others’ tweets.
These things are harmless; they’re good, healthy activities; but they do not a full life make, and they are all addictive. The Internet is a great connection machine; there are always more people to talk to and more things to read. You could spend your entire life on the Internet and never reach the bottom. Some days, I want to; wrapped up in reading (for example) articles about Cocoa, it’s very easy to forget the homework that’s due tomorrow. These harmless and positive activities then become as detrimental as any imbalance-creating addiction.
That said, the wonderful thing about addiction to the harmless is that you don’t have to give it up to get better. Once moderated, these addictions become an important and wholesome contribution to a healthy and balanced life. If I can do it, and I can, then you can, too.