I have only watched it once from beginning to end, and that was the year we did it here in this forum, when the DVD sets were coming out. What was that? 2003 or something?
I watched it's initial run on TV from the first episode, but I was in Russia all of 1995 and so missed about a year of it then, and then missed the odd episode once I returned.
I was later able to see the episodes I missed from 1995 when the VHS tapes started coming out, but I was never able to see a couple of the latter episodes which never came out on tape until the DVD sets came out.
Anyway, the year the sets came out we watched the entire show as a forum from beginning to end, and that was really fun. And since then, I watch an episode or two here and there when I feel like it on DVD...and I would often walk on the treadmill at night to DS9 on SpikeTV when it was on.
I should really watch it from beginning to end again. I've been missing it lately.