For someone who spends so much time online, I actually don't log my mileage electronically. I have a dailymile account, which I used for a couple months but it didn't really provide the info that I want. I'm not that concerned about how many km I've run in a week, I need something that will show me what I've been doing, and show me at a glance.
I've recently started recording everything on a calendar:
If I have done a quality session, I also write the details in my notebook so that I know what times I ran, and what the session actually involved. If I don't have my running notebook with me I often write the details in another notebook or my diary, then transfer it across when I get a chance.
I also have a card file where I write down session suggestions. I used to always read sessions in magazines and think they looked good, but I would never remember what they were. I'm much more likely to do speed work by myself now, because I've got lots of sessions to choose from. I'd much prefer to do these sessions in a group, but it's just not always possible.
At the end of the week I add up my mileage, but I don't record it. I don't think it's worth running more just to make up the numbers!