May I be so bold as to say there's an undertone of (good-natured?
) disgust at using the FMS to plan a descent in some posts.
Don't get me wrong, I FULLY AGREE that you shouldn't need it (and I don't) but it is there as a great resource for 99.99% of the time on the type the original poster is flying and, at a quiet airfield with little ATC intervention, it is great at planning an efficient, continuous descent for minimum fuel burn, taking into account it's extensive knowledge of the aircraft's performance, minute to minute.
As I allude to in my first post, the FMS is a great tool on the a/c the poster flies and making use of all resources is surely what every good pilot should be doing? I don't rely on the FMS though, hence the ballpark figures/rules of thumb that everybody mentions always being at the back of my head. In my humble opinion, as long as you don't end up blindly following the FMS and have made the effort to learn exactly what it's trying to do at every point, it can only enhance your situational awareness and not detract from it.
A bit of book work learning about exactly what the FMS is trying to achieve in each mode/phase gives you a great overview of the way Boeing obviously suggests things should be done on a particular type and is an invaluable grounding on which to add some finesse yourself.