Playing with it on a Commodore 64 emulator, I can kind of see the appeal. Writing equivalent programs in BASIC vs White Lightning Forth, the Forth version is substantially faster, without being that much more difficult than BASIC once you figure RPN out.

I used an HP calculator in high school and use an HP emulator on my iPhone, so I'm already pretty good with RPN, so the weird syntax is coming fairly natural to me, and it's substantially easier than doing everything in raw assembly.