Pierre, please note I'm not insisting on immediate removal of these instructions (oh, I could remove that control from my site without much trouble if I will want it). I'm more trying to add a point to think of. Adding new features by brute force is not the best way to handle things, it may add more bad then good points. Asking for something people not always thinking about the consequences (there are too many examples), and in case of bad consequences they will blame Moodle (you), not themselves for asking.
The number of fields in question editing is really growing, and that is worrying thing. The are many questions, and editing them should be as quick as possible (it's OK to have a long form to edit quiz, there are few quizzes, but much more questions....). Should we really mindlessly associate all new features with the questions as objects? Remember, if you place a field too low in hierarchy you'll get two problems:
1) you slow down editing of (questions);
2) you should repeat one information often, entering same things againg and again - not really the thing people appreciate often.
Let's take a units for example. Are particular units a property of a question, individual question? Is a multiplicator between pounds and gramms different for different questions? I really have my doubts about it.
Of course, sharing need to be carefully thinked out. It is just easier to add all to the single questions, and let teachers/authors suffer from this. Thought it probably naturally easier for units, when you could define quantity, and then all units of this quantity, while choosing in particular question only quantity, desired units and mode. And so on...
There are things that is easier to do for you interface for now. For example, you could use drop-down menu instead of long list of radio boxes when choosing unit mode for a question (and for choosing units in attempt too, drop-down menu will place unit exactly after the number). And some controls on the form could be advanced too...