As a kid, my parents bought all the DVDs of season 1 from a friend. My sister and I watched them alll day. From then on, I was hooked. Pretty sure I watched up until Advance Generation regularly, then only Sinnoh and the newer seasons on my own. My sister wasn't so hooked, pretty sure she stopped whenever I stopped watching them on the family TV.
My brother is a huge fan of the Pokemon games but I don't know if he's ever seen the anime, really. I think he's maybe a little bit familiar with it but I doubt he's seen a whole season... I have no idea actually.