Yes—the email list is open to all ACCU members. Observers are always welcome. We’d really like some more mentors. It’s still not too late to join in as a student either, and more students would be very welcome. By reading the email list archive you can get an idea of what all this involves, and also catch up with the exercises you’ve missed.
I can only provide a personal answer to this question. For me, it has much to do with a growing interest in computer languages, and in Lisp in particular. As Kevlin Henney writes:
Many programmers develop an infatuation with Lisp at least once in their programming lives. If you haven’t yet, now is your chance.
I’m quoting Kevlin out of context—he’s not talking about the chance to study SICP with a group of like-minded people, he’s introducing an article which provides a C++ implementation of Lisp-style list processing. Perhaps this is the conventional reason for studying Lisp: you may never use it in anger (how many job adverts are there for Lisp programmers?), but it will inform you and make you a better programmer. Thus Eric Raymond advises would-be hackers:
LISP is worth learning for a different reason—the profound enlightenment experience you will have when you finally get it. That experience will make you a better programmer for the rest of your days, even if you never actually use LISP itself a lot.
Paul Graham, though, goes further. His book, “Hackers and Painters”, was what really urged me to find out more about Lisp. In this book, Graham describes Lisp not as a language to be learned as an end in itself, but as a superb language for designing and writing computer programs.