All the best answers have already been said.

It's a single-player game, and one that is very open-ended. Cheating is mostly defined by the player, I'd say.
Even Cinco's viewpoint can become a grey area, especially if roleplaying is involved, and we happen to see our characters as seperate from us. If I go on UESP to figure out something, I might personally see this as a cheat, but what if I'm roleplaying a character who's got knowledge on certain subjects that goes beyond mine?
For example, I've got a Crusader who's supposed to be an expert on Aedra and Daedra. I personally don't know much about these, so sometimes if I get stuck on a question (regarding a quest, and related to knowledge of daedra and aedra) I will have a look at UESP.

I learn something in the process, and as long as I don't read about the entire questline I'm doing, I don't feel it's a cheat if the knowledge I gain from UESP happens to help me solve a portion of the questline.
Personally I feel that sitting there and reading an entire quest (giving yourself a myriad of answers) is cheating, especially if the gamer blows through entire quests this way, and then comes HERE boasting about how "easy" or dumbed-down the quest is. Same thing goes for non DiD gamers who complain about how easy the game is, as they attack the same enemy over and over because they keep dying.
I also never touch the difficulty slider, especially during combat, as I
personally feel this is cheating. I have bumped the slider to the right, though (making the game more difficult).
Cool thread. It's good to see folks discussing these matters in a civil manner, too.