1- I find the recursive deletion highly "dangerous". I hope it's protected behind at least 2 confirmation boxes.
2- In general... could we start using some sort of execution_result class or so in order to return functions execution results? I can imagine this functions (or similar) as potentially being used by web-services or so and separating process from output could be a good idea IMO.
3- There is one return false missing the corresponding notify (the first in category_delete_move() ).
4- Not knowing internals very well just want to notice that, when category_delete_move() is used, courses aren't deleted, so they can be using questions, so IMO questions should be moved to parent cat too, instead of deleted. For sure Tim or Jamie will confirm this. In the other side I think it's safe to delete questions when the category_delete_full() is used, because courses (potential uses) are deleted. Needs confirmation too.
5- Perhaps it would be interesting to leave some records about deletions in log table?

Ciao

to Jamie:
the parent category is not used here anymore - they are either all moved to new selected category or deleted

function question_delete_course_category($category, $newcategory, $feedback=true) {
$context = get_context_instance(CONTEXT_COURSECAT, $category->id);
if (empty($newparentid)) {

I also don't think that you should be doing:

delete_records("question", "category", $category->id);

after

foreach ($questions as $question) {
delete_question($question->id);
}

There is a reason why the code

// Do not delete a question if it is used by an activity module
if (count(question_list_instances($questionid))) { return; }

exists in function delete_question.

If there are any questions left after the for loop, then you should set them to be hidden, and move them to the default site category, or something.

sure silly bug caused by refactoring, should be
if (empty($newcategory->id)) { // means user requested full category delete including all activities, courses and categories

I do not understand why you would be moving the questions to anywhere when deleting everything in course category.

return set_field('question_categories', 'contextid', $newcontext->id, 'contextid', $context->id);

Is the subquestions are also moved or not ?
see MDL-10899

$questionids = get_records_select_menu('question', 'category = ' . $category->id, '', 'id,1');

Some thoughts:

• Don't embed <br> in the new strings. It can be shorter anyway: "If you delete this category, you need to choose what to do with the courses and subcategories it contains."
• I got the confirm dialogs even when the category was empty (brand new)
• "Confirm category delete" menu is a bit odd (both as a UI thing and in it's wording, because it applies to more than categories), could go completely.
• "Delete" fieldset could be called "Contents of $categoryname"
• The second feedback screen has some issues:
  a) it shows empty table headers even where there are no questions involved at all
  b) Category in this case means question category (not course category). Needs to be a lot clearer, say "Question category"