Had a bug with the Dark Cave tonight, as I was going to go in and wreck the bosses. :>
If I declined to enter the cave, after talking to the NPC at the entrance, cloud turned around as expected and what not, I could however not move him or anything, but the rest of the NPCs along with the music, carried on like normal.
Also had to sell a bit of materia to enter the Dark Cave, without worrying about losing crucial materia, which isn't all that fun, but I suppose I may have more materia than the average player at this point. :>
Edit: Not sure if I've mentioned this before, but you can encounter Cid in the wallmarket bar, before re-obtaining his services, making him appear both here and in Tifa's bar.