Born in 1965, I did not really see TOS in its first run, but became a fan via TAS in its first run and during the glory days of TOS syndication, mostly via WPIX-11 in NYC. My youth was of course my most obsessive time, with books, fanzines, and seeing Shatner on his college tour in 1976. Basically watched all the time through my teens and into college, and went to every TOS movie premiere. Saw TWOK in the theaters about a dozen times. Read some of the early "giant" novels.
I was full on with TNG, but quickly lost interest. I stopped taping it (Betamax!) with "Code of Honor," and did not resume watching until Season Three was in reruns. Then watched it fairly regularly.
Started in on DS9, and was taping it and TNG again (VHS) but tapered off with DS9's second season. It didn't quite grab me at the time.
After that is when it was on and off a bunch, mainly because life happened. I missed almost all of Voyager in its first run, but caught the first couple episodes of Enterprise, but it didn't grab me, and I was a little put off by the look (I was unrealistically expecting some sort of Forbidden Planet kind of look).
It's a little bit of a blur what happened first. I know Generations was the last Trek film I saw the premiere for, and Insurrection was the last of the TNG movies I saw in the theater (the parts that I stayed awake for, that is).
I was still a fan, and I would watch now and then, and I bought each new format of the TOS episodes as they came out, but I didn't get really back into Trek until 2006, when "Crucible: McCoy" was published. This amazing novel and subsequent trilogy brought me back to the novels. And then I decided to watch the shows I'd missed in order to "get" some of the newer books. So over the next couple years I stalked Ebay for DVDs and eventually caught up on the shows, with Voyager's finale being the last. I watched Enterprise earlier because I found it cheaper first (and still like it more, TBH).
It really kicked into gear when I joined this forum and Facebook, and hit new highs when the new films started appearing. I still don't watch a ton of the shows (mostly TOS) but I'm reading the novels and comics, attending cons, building models, etc