In a sense, yes, game guides are ruining the time people spend playing games.
(And this isn't meant to be a FFXI post, I think, but as a question about GAME GUIDES, it naturally will include FFXI, along with other FF's, and other games. Not every post that includes the words Final Fantasy makes it a stupid-post.)
I've heard (hearsay only) that actually - if you talk to enough NPC's, you'll get all the information you need to know about where to go and what to kill.
In most RPG's, I've noticed, if you have the patience, someone, somewhere, will let you know what you need to do. It may not tell you what the reward is, and for people who know that Aspir is out there, they want to get it and they want to get it now. That is also a reason why I think people in FFXI advance "too fast" for themselves. Instead of doing all the quests possible in a town to get all the possible items... they just do the ones they want (then wonder why they don't have enough fame to do other quests).
For other games, we tend to buy the game guide - but, my husband insists on beating the game one time through by himself, to discover everything there is by himself, to be surprised, and the like, and then he'll go back and beat the game again with the guide to get all the fun hidden things he couldn't find the first time.
Other games, non-RPG games, I don't really see how having the guide can hurt anything but your wallet. In Diablo II, we have the game guide, just to look through it and read about the characters, to look at all the items that never drop for us, and the like. You don't really need a game guide to get you through that game though.
We have the Animal Crossing game guide to let us know about what special days are, what to look for, what furniture sets there are, and what to fish and when.
I'd like to get the Harvest Moon game guide, too. :P
But, overall, I think getting a game guide is a symptom of our personalities.
Some people are happy doing it themselves and want to do it themselves. And they will spend the required hours figuring out what to do and how to do it, fighting and dying several times until they succeed, and then leave feeling a sense of great satisfaction.
Other people know that dying over and over without them figuring it out will merely frustrate them to no end, and so they go with the game guide, look up everything and are like Batman, prepared for every thing that could happen to them, and they beat the game or do the quest and leave feeling a sense of great satisfaction.