I observed to C. that I was having a week full of meeting LJers, and he shook his head. He preferred the version of my week where I was meeting lots of friends-of-friends, because that's true too. It's just that they all happened to keep weblogs, and I'd already interacted with some of them beforehand (austengirl, genibane). Or not (tjej, lady_ceres, schiehallion, fox_c). They may all have usernames, but those are largely incidental to my acquaintanceship, for we all have off-line, long-term friends in common too.
That's been true most of the times I've met someone who I knew primarily through online interactions. I met double0hilly, saffronjan, and cliosfolly through respectable academic conferences; except I already knew them. I would have met littleowl and maxineofarc when I started at my undergrad university, whether or not we'd already corresponded extensively in other ways.
From the right vantage point, my fellow webloggers are my penpals. (Keyboard pals?) We write open letters, which are most frequently read by our most regular correspondents. Once in a rare while, some of us meet in person, often after a long period of writing back and forth in various ways. In contrast, my first penpal arrived in my life in a whirlwind of opportunity. She was in France when i was in high school. In her second letter, she asked if she could come visit, on a multi-student exchange trip between our two cities. We accepted, despite doubts as to the speed of the development, but it worked out beautifully enough that I went and stayed with her family for a few weeks less than a year later.
Thank you for writing your letters to the world (or some subset of it). I like reading them, and I keep posting these days because it's a very easy way to write back.