i worked in APL2 fulltime years ago, big asset backed bond models, big as in some of the largest workspaces the IBM support people had ever seen. Never occurred to me to pick it up again, but i have been looking for the Polivka/Pakin book i learned out of (the edition prior to their APL2 edition).
However, what got me to invest in earnest study was hitting today beginner's wall and realizing that I had no idea what Iverson was on about with his design principles.
APL is really different these days, as far as I hear. Dyalog APL is the only vendor actively working on the language these days, and the old hats tell me that things like dfns, trains, and various operators make modern APL quite different from APL even just 15 years ago.