This is a great question.
When I was younger -- during the SNES/N64 years -- I had no qualms about using guides. I think I still have my Ocarina of Time player's guide lying around somewhere.
Now, however, I can't bring myself to look. I have this compulsive need to figure out something myself, no matter the mental toll it takes. Looking at a guide does "ruin" the experience for me, a little.