All day, basically. I turn it on after feeding the dogs/cats in the morning, and turn it off when I go to bed at night.
Since we recussitated the old laptop, I often have both the downstairs and upstairs computers doing something.
I don't like to talk on the phone, I'm not terribly social in real life, I can go days, weeks without TV. I could probably even lose my TV altogether without trauma, but if the internet goes down for an hour, I feel stranded on a desert isle.
My husband and I met online in April 1996, married in May 1996, and for the first six months of our marriage were forcibly separated by an ocean, thanks to immigration laws. To be together, we spent all day online, and it's been interconnected with our daily lives ever since.
I don't consider being online itself as an addiction, though I have experienced addiction to some online activities (the first 2 years online on IRC, chatting; Runescape; etc.).
For us it's just a normal extension of our participation in the world.