If I recall corectly they are not that hard to adjust, but are a real bitch to get to. I think you may even have to drop the motor out. Take this with a grain of salt. I don't own a Duc and don't know that much about detailed sevice of them.
I do believe that some of the older Desmo motors required an adjustment every 3K. My g/f had a '96 900SS/CR and that was what was in the owner's manual for scheduled maintenance. My '99 is every 6K. I heard that when the Texas Group took over, they addressed some issues with the valvetrain and this might explain the additional time between adjustments.
I hope that after I die, people will say of me: "That guy sure owed me a lot of money."