I just use YouTube for watching Star Trek related videos, I wouldn't be able to see otherwise. I own all the shows on disc, so wouldn't dream of straining my eyes for whole episodes. I do upload rare footage ommited from DVD release though... old VHS trailers, unreleased documentaries and interviews.
I used to be into that whole torrent thing purely for brand new episodes of Enterprise, because I simply couldn't wait the many months they took to cross the Atlantic legally. If in the future, a Star Trek premiered on the web before a TV broadcast... CBS would no doubt have my custom.