Yeah, that's about when it changed. The lack of a wall was a very early situation. I joined in 2004, back when it was only open to Ivy League and Boston-area schools.

It was still acceptable to write on someone else's wall when they came to be called that. You can still do that now I think but it's quite uncommon and how it works is now complicated but settings.

Sure, you could. That wasn't the problem. The problem was that now you could post on your own.

That's what turned it from a method of reaching out and sending messages to specific people when you had something to say to them to a means of shouting into the void and expecting (or at least hoping) that someone, somewhere, would see it and care what you had to say. It went from something actively pro-social to something self-focused.

Blogs and other self-focused things already existed, but almost nobody used them for small updates throughout the day. Why do you think the early joke about Twitter was that it was just a bunch of self-absorbed people posting pictures of their lunch? Nobody knew what to do with a tool like that yet, but the creation of that kind of tool has led to an intensity of self-focus and obsession the world had never seen before.