Worse, they punted on what for me is the essential Eudora feature, a multiple document interface (MDI, see e.g. http://en.wikipedia.org/wiki/Multiple_document_interface). I personally like both filters and knowing when I've gotten new email that was filed into one, keeping some emails open until I deal with them, etc.

No substitute for the real thing.

And Wozniak is correct about how useful the arbitrary button feature is, but I'm pretty certain Eudora isn't the only email client with scripting ability (EMACS for sure, although I transitioned from rmail back in 1996).