I would consider it a form of cheating if the game required large amounts of brain activity such as most point-and-click adventures, though if you use a walkthrough for one of them your mostly cheating yourself as I've always found part of the fun of a PaC game was the satisfaction of figuring out a puzzle on your own brain power.
In more typical adventure games such as Zelda I normaly only use guides as a last resort, or use them on a second playthrough in an attempt to get 100%, but then again it also depends on the game. I remember a last gen game called 'Sphinx and the cursed Mummy' which although it was an exellent game, was totally useless at providing any hints at where to go or what to do next and I had to use a walkthrough quite a lot. If a game has issues like these I would have total sympathy for someone useing a walkthrough for most or for the entire game.
