I remember quite clearly, it was a big thing then. If anything, bigger than now (in that small changes to one's own content, and small manipulations around linking, could have big effects on the major search engines). Back then, SEO was about careful manipulation of <meta> tags, keywords, tricks like filling your page with white text on a white background so the search engine would see it but not users, etc.
I'm not sure what SEO is about now.