While I understand that the use of a walkthrough is a personal decision, here's the problem I have with them:
-Adventure games are supposed to be a challenge. The developers went to a lot of work to make them so. Consulting a walkthru at the drop of a hat seems to me counter to the whole idea of the games.
-IMO, it's very hard to use a walkthru just a little bit. Once you start using them, I think it gets too easy to avoid solving a difficult puzzle or challenge.
-For me, the use of a walkthru destroys one of the great benefits of adventure gaming: the feeling you get when you solve a really difficult puzzle or situation that may have taken hours to figure out. When that happens, I get a 'puzzle-solving high' that lasts for days!
-My biggest gripe about the use of walkthrus is to hear people complaining about how few new adventure games there are and then hear people say that they just played a complete adventure game in the last day or two. Since I often know how difficult the given game is, I also know that they likely played the game from beginning to end with a walkthru and something about that just bugs me!
So, I have never used a walkthru, but I have used the very occasional hint from UHS.