I've recently gotten more serious about weight training (had an appointment w/ trainer yesterday) and though it's too soon to say how much it might help with my various arthritic joints, as discussed on
this thread, weight bearing excercise is a very important adjunct to our bone-density-sapping sport.
As I mentioned there,
Bike For Life, by Roy Wallack and Bill Katovsky -- is a good all round guide for those who plan on riding to 100.