Comment by kqr
This is a common myth, but from what I understand of people who write in the more logical shorthand systems (without abusing custom abbreviations etc.) it's eminently skimmable, even long after the information is no longer fresh in mind.
I don't know what you'd consider the more "logical" systems - there are only a few non-machine English shorthand systems with any degree of popularity. My own experience with Teeeline shorthand (which is a bit easier to learn, and I'm by no means good) is that I simply can't read quickly because I don't get much reading practice. Think about it: most of us read much more than we write. With shorthand, I only end up transcribing what I myself have written. So I'm slow at it.