Actually, if you use a tuner (and your guitar's intonation is set as standard) then you are putting your guitar into even or equal temperment, so it will sound just as crappy no matter what key you are in. if you use a tuning fork for one string and then do the 5th fret unison mehtod of tuning your gutar, the results are the same(or at least very nearly) if you use a tuning for for one string and then use open strings and natural harmonics and getting rid of all of the beats between unisons, then you are putting it in more of a type of "well" temperment (term taken from piano tuning practices) in which it sounds more in tune to the ear, in some keys, and more out in others, but over all, any key is acceptable. SOME people that i have encountered use a tuning fork, or a tuner or whatever, and then for what ever song they are playing, go along and make little adjustments to help them out with whatever key they are playing in, so that for instance, a certain chord that is hit repetedly will be exactly in tune, however, other notes on the adjusted string might be out a little. This method has alot of potential, but you have to be really careful, or everything you play will sound like dirt, except that one chord, or whatever.For CG I only use the classic tuning-fork. Tuning a CG is not like an electric guitar in my opinion. It´s a compromise. If I would use a tuner I could get all the strings to tune individually perfect, but it would still sound crap in a different key. (I guess this post belongs in another topic).
so there you go