pros: low maintainance, clean, quieter
cons: heavy, sap power, torque reaction (more on this later), when they do go wrong...........ouch, gearing is set..........forever.
shafts usually run inside the s/arm and the pivot point is quite close to the 90' bevel housing. this means that a % of the power is created as lift! which means that the bike actually lifts when applying the throttle, changing ground clearance, steering geometry etc. conversely when you close the throttle, you lose clearance, give it the wheelbase of a chopper and usually a 1 way trip to a&e if it's your first time on a shaftie.
BMW came up with the ingenious (and heavy, and expensive) paralever system which goes a long way to eliminate torque reaction, but not totally.
on mine i had to replace the paralever bearings (twice) and surprise surprise they are bmw only items and bloomin pricey!
ex Z1000ST and BMWR1100S owner
(oh, the GS1000G was just an overbored 850, not a real 1000!)