Thanks to Matt‘s link earlier this week, several new people found How to Japanese, including Akaki who knows a thing or two about 変換! He provided a bunch in the comments. I’ll repost them here.
Also 郵便（ゆうびん）＝〠 (look at the guy!)
平方センチメートル＝㎠ (note how the exponent is actually part of that single character)
“Oh and あっぷるぱい＝π :)”
I love the fact that all the units can be compressed into a single character-space – clearly useful. I wonder about the era names, though – you’re only saving one space! Cool to see that Apple got into the action by creating a kotoeri-only 変換.