Something I discovered and thought it might be worth passing on. If you want to preserve your well developed callouses, DON'T get into a habbit over a protracted period of time playing your guitar capo-d up two or three frets. I'd been doing this the past several weeks as I was working out different flat and fingerpicking runs.
In preparation for a get together today with a friend and to do some pickin', several days ago I took the capo off of the instrument and started playing things in the first three opened positions, and for the life of me couldn't figure out why the ends of my fingers (fretting hand) ached. I'm feeling the ends of my fingertips thinking where the f--k are my callouses? Apparently playing in a capo-d position on a regular basis destroys them, and because the action is so low, you can get by with a feather light touch and your fingertips don't get the regular workout they need to maintain the callouses.
So take that capo off and play in regular positions frequently. Your callouses will thank you, and you won't have to go through the process of rebuilding them.