I cheat when I want to cheat, that is, usually when I buy a game I play it once to completion without using any guides at all and then if I am still interested in a game it is usually to mess around in it, try things I have not tried before and seeing what is possible.
This is why I don't tend to like hack and slash or platform games as they are only good for exactly one playthrough using these criteria.
With a game like New Vegas, I know it through and through now. So if I start a new game and there are shortcuts I can take to achieve a certain goal faster I will take it.
I don't know if that is 'cheating'. I would like to hear more about this double perk thing, google is less than helpful.
I never saw playing around with the mechanics in Morrowind as cheating, even when I created godlike spells and abilities. I had earned that, by virtue of learning the game mechanics so well I knew exactly what would work and what would aid me.
Things like using a cheap drain skill spell to use trainers very cheaply I never saw as cheating. I saw it as a smart usage of the tools available to me and something that I had very much earned by figuring out it would be possible in the first place, something which requires an intimate knowledge of how the game works and which is not normatively available to a player the first, or even third, playthrough.