I've technically been playing since Vanilla but never interacted with the community because I couldn't even join any of the internet servers that were up.
It was the February that retail was released during or right after.
I kind of gave up on vanilla because I thought it was too hard to build, having to actually pick up your bricks before you use them, but then came back in March with a "I bet I can do this now! :D" attitude and found that "there's this crazy new version of the game with better graphics and easier building". I was surprised to see that the online play actually worked after I bought it considering it was broken for me in vanilla and stuck around because it was a lot more fun than vanilla.
And that was still before there were really any add-ons. I didn't know there even was an add-on system until I joined a freebuild and found Kaje's stunt plane, and I'm like "OMG! what is that??? can you drive it???"