First, rosewood fretboards don't really dry out where it counts, since PRS has already purposely gotten as much moisture out of them as possible - for good reason.
Rosewood does, however, have natural oils that stay in the wood. The evaporation rate on these is incredibly slow - and your hand oils are sufficient to keep everything fine and dandy.
Lemon oils are actually naphtha with a lemon scent. They are for cleaning the fretboard, only. Naphtha is what your dry cleaner uses to clean your clothing, because it evaporates, taking the grime with it. It does the same thing on your fretboard - it evaporates, taking the grime and oils with it as you rub. The idea that a fretboard gets "oiled" by it is just not true. It can draw oils in the wood to the surface, however, that's the opposite of what one wants.
PRS recommends using the lemon oil to clean the rosewood fretboard, wipe it off, and then seal it with a regular furniture polish. As I understand it, this is what they do even in Private Stock (I believe they use Behold). If your hands leave a lot of residue you might need to clean it more often than I do, mine stay fine for years.
All of the food-based oils (and this includes what's incorrectly called rosewood oil) only rot in the pores of the wood. They do nothing for the guitar, and in fact, can screw up and soften the fretboard, which is not a good idea at all. "Mineral oil" is absolutely the worst, put it on a fingerboard and you can literally dig up the wood with your fingernail.
Sometimes less is more.
As to care of the body, it's all about preventing cracks, though a PRS HB has been purposely dried, it's not gonna hurt to keep the humidity around 40%. PRS told me that the factory runs the humidity at 40-50%.
In the winter when it's dry in the house, I keep the guitars cased and in a humidified room at around 40% RH (more than that tends to be clammy in winter). That's really all the acoustic instruments need to stay in tip-top shape, and a hollow body electric should do just fine, but if you're super-paranoid like me, you could throw a Planet Waves humidipak in the case (with the cases for electric guitars there's usually an open area near the neck or headstock). These keep the RH in the case around 40%, and I find that the necks even on my electrics need less maintenance since I started using them. The beauty is that you can't over-humidify with these things; they absorb excess humidity if it's too humid, and release humidity when it's too dry. I started using them year 'round about a year and a half ago (thanks Cory for the tip), and no issues at all.
