Very good thread, Rick!
I want to agree 100% with Mark C about learning to tune by intervals. My wife is a violinist who is well versed in this method of tuning. She can tune up my guitar in about 10 seconds, whereas it takes me minutes. I am a relative beginner, and here is the way I have been doing it. I tune the "A" string to a tuning fork as Mark describes. Then I sound the "A" and (try to) sing the "D" one fourth higher. Then I fret the "D" on the "A" string and try to match it with my voice and try again. When I think that I have it, I tune the "D" string to the "D" I sing. Then I play the "A" and "D" together and fine tune so they sound "right" together. I repeat this with all the higher (in pitch) strings. Finally, I tune the bass "E" to the treble "E" by playing them at the same time until it sounds like one "E". Then I take out the electric tuner and see how I did. Nowadays, after doing this for about nine months, I am usually within ten cents of the tuners opinion. I think it is important to have a tuner, wife, or teacher who can tell you when you have it, else you can learn to hear things wrong. Eventually, I hope to do away with those intermediate fretting steps and just sing the intervals to myself.
About what Art said about waistlines and what Rick said about size of guitars. If you have a larger waistline (like me) you will have more trouble playing a guitar with great depth. That is where one with a larger body size and less depth (to get the same bass response) is good--for example the Martin "OM" shape. I solve the problem by holding my guitar in a classical position. That is with the waist of the guitar resting on my left knee which is elevated. I think you get better left-hand mobility that way anyway. If the body is too big, though, you have to hold your left hand too high for comfort.
As Rick says, there is always a trade-off.