Levels of Distractibility: Who cares? = *. Some people will be distracted from your meaning: = **. Many people will be distracted from your meaning: = ***.
Question: Which is it: "tablespoonsful" or "tablespoonfuls"? "Teaspoonsful" or "teaspoonfuls"?
Answer: I never can remember either. I guess "tablespoonsful" would mean using several tablespoons at the same time. That doesn't make much sense. So it's one tablespoon that takes three tablespoonfuls of sugar. Same with "teaspoonfuls."
Rating of Distraction: (*) in speaking. I doubt if anyone gives the distinction any thought. Both versions are jawbreakers--UGLY. Logic, though, does suggest that it's one teaspoon which takes three "teaspoonfuls" of sugar. (**) in writing.