> Pi - good one, I have seen this used for sets. (You have to pick up your pen twice.) People don't want to use it to do actual hand calculations, and so rarely use it in papers (both because they aren't used to it and, perhaps, because they know their readers won't want to write it by hand). This one is fine to typeset, but is slow to write by hand because it has three disconnected strokes. Generally agree, but should be supplemented with influence of hand-written math.
