From my perspective, it was their embeddable video player. You'd see it pop up in other sites, spreading the YouTube name on external sites the web-over. I reme

From my perspective, it was their embeddable video player. You'd see it pop up in other sites, spreading the YouTube name on external sites the web-over. I remember thinking that capability was extremely cool at the time (and built off things like iframe chatboxes and embeddable hit counters.)