A word of warning for Elisp hackers: the Emacs Lisp part of that resource was written by someone with a CL background. I'm seeing various examples that are not conventional Elisp. For instance, ' is used instead of #' for function quoting in various places (prevents compilation of the function) and use of eval on a form instead of apply on a list (dangerous and also prevents compilation of the form). In addition, many of these features use the cl package at runtime, which will cause the compiler to throw a warning, because it's not allowed in Emacs proper.

That said, there's a lot of information here that's very useful for the starting Elisp programmer.