I try not to... but I hate the feeling of knowing I'll possibly miss out on some big secret item or quest because I didn't inspect that unconspicuous wall tile aaaaaall the way over there instead of just walking towards the exit. Then I read about it months later and I'm all like >:(

But I figure I've looked at a FAQ for just about every game I own at least once. I don't like being kept in the dark.

For some games, I don't care. Especially for Pokemon where I see the ones I love and immediately figure out how to construct me team and how to manage until I fill out the team.

And I'm still annoyed about the Zodiac Spear trick.

I only use guides if I'm truly stuck in an area. Otherwise, I do my best to avoid them. Sometimes though, I just buy strategy guides for the prettyful pictures. Sometimes it really is handy to have the book in hand if you wanna see a head to toe shot of a character you want to draw. 

My usual approach is thus: I'll plough through the game unguided and get to the end, and then and only then check out a guide to see what I've missed - if I did miss anything, that is. And that's only if the game itself doesn't give me a hint.

The only exception to this is if I happen to get hopelessly stuck somewhere with no clue whatsoever how to progress. If that should occur, then I might consult a guide. I generally consider this to be poor design if it happens - the means to solve a puzzle or get by an area, in my opinion, shouldn't be so far removed from the norm that it's next to impossible to figure out. Unless that's the whole point of the game, like some of those Flash-based puzzle games I've seen.

In a nutshell, I only consider using a guide cheating if you've not already beaten the game before.

Complicated answer.

My family subscribed to Nintendo Power during our overseas years, which was one of the few ways that we were able to stay in touch with the gaming world at that pre-Internet time; and during those earlier years of it, NP was pretty much a cheat guide for multiple games with a lot less advertising than you would see in a modern version.  It didn't seem unnatural to get gaming guides for certain games I really liked, like Super Metroid.  And some games like Donkey Kong Country would have taken forever without the aid of a guide of some sort.  Pokemon, a guide was required because I always wanted to try to catch them all - and that seemed to be the only way to be sure.

Fast forward to more recent years.  Pokemon's Pokedex system makes it possible to track down Pokemon you've seen in battle, so it isn't that hard to catch them all.  And GameFAQs has almost utterly annihilated the need to buy a game guide when you can just look it up for free online; granted, info on some games can be scanty or poorly-written, but that's rare on any decent game worth playing.

I don't see anything wrong with using a guide to help past difficult parts that aren't very intuitive in a game.  I'd rather be able to beat the game in a reasonable amount of time rather than, say, get frustrated because I've tried virtually every combination of items, spells, tactics and just hitting things to the point where I hate what would otherwise be a fun game.  But for the most part I've been a gamer long enough that I recognize most of the tricks and tactics that game developers use, so it doesn't usually come down to that.

I tend not to use them unless I'm impossibly stuck and I've exhausted all other options. That being said in a game like Zelda that's heavy on collectable items, I'd prefer to have an idea of what I should be looking out for and how many of them there are - I'd hate to get to the end of the game and feel like it's incomplete because I missed a Poe that can only be grabbed once, or something.

I use a guide whenever possible, and really, I have no idea why. I mean I could beat most games without the need for a guidebook, but I guess I just like to know how to beat a boss, etc. without going through trial and error. Also, with RPGs I like them to find the items, weapons, etc. though I hardly 100% any game.