It's like "how much do you drink/smoke?" I find I have a tendency to understimate.
I put 4+, but if I rally think about it, it's regularly more.
Usually I'm online for at least an hour before I go to work at 8am. I return at 6pm and switch on my computer before I take my jacket off. I'll be online 'til at least midnight.
At weekends I sleep later but usually I'm on for about 12 hours a day.
So over a week I'm online for about two and a half days plus.
For a guy who doesn't work in computing or even use a computer at work, that's getting to look a bit pathologigical