I still don't own any TOS (or any other kind of Trek) on DVD; it's all on VHS. I have the movies on commercial VHS, a couple of blooper tapes, and a few episodes. The rest I taped myself. I remember my old Star Trek club meeting at my place a couple of times a month for watching (I was the only one who had everything up to TNG at the time). We literally wore out the first-season TNG tapes from watching them so many times!
My clearest memory of watching The Trouble With Tribbles was when we noticed Kirk apparently changing clothes in the turbolift. He got on wearing one shirt and got off wearing a completely different one.
I'm going to have to get the DVDs, though, since my tapes are wearing out and I'm running out of room to store them. Even putting 6-8 episodes on one tape takes up a lot of physical space!