The first time I saw im@s, I probably didn't realize it was so. I think I eventually learned of this "idol simulator" game that was floating around, but I never paid it that much attention. Since it was roughly the same time as Hatsune Miku and VOCALOID getting popular, I just lumped them together. Cute-looking virtual idols, no big deal.
Then there was Kumikyoko Nico Nico Douga, that famous 11-minute song that began with Ami/Mami's version of Agent Yoru wo Yuku.
http://youtu.be/0-x6R0mKzII Except I still didn't know it was im@s at the time. I only recognized Haruhi and maybe AIR and another.
Xenoglossia I pretty much ignored; I knew it was some sort of spinoff and that people didn't enjoy it that much. It also seemed a lot more fanservicey than I cared for at the time.
It took until episode 4 or 5 of the anime really, lol, before I finally submitted. When the anime came out, I started downloading episodes to put in my queue but did not watch right away. I think I gave the first half of ep1 a chance one evening, but the pacing didn't really grab my attention. Then some weeks later the Internet went out, so I was stuck and decided to watch some things in my queue to pass the time. I gave episode 1 a full go, and by the end I saw a little bit of magic and thought it was cool how that was the way Producer introduced himself. (I think it was also partly friends on IRC talking about the anime a lot, so I felt like I needed to keep up.) I still didn't know everyone's names yet, but it was interesting enough to keep on. So through eps 2, 3, and 4, I learned as much as I could and grew to love it. I needed some new music on my playlist anyway, haha, and there was tons of it available.
So when episode 8 finally came around and Agent Yoru wo Yuku started playing, I was like "I KNOW THIS SONG" and finally, several years late, made that connection. Rest is history, I guess. And I committed further by spending $281 on the PS3 special box. :3