I have followed Sacha for a long while, love her frequent Emacs updates. I am a rabid Common Lisp enthusiast, and I bought the Mastering Emacs book last year, I just need to pull the trigger and try doing a project in Emacs Lisp.
I did it the other way, and going back to elisp is /hard/.
In practice, everyone writing new projects uses it, but when you choose to interact with existing code...