From Programming Erlang, by Joe Armstrong, chapter 1, "Getting Started":
Did you actually run the shell on your system? If not, please stop and try it now. If you just read the text without typing in the commands, you may think that you understand what is happening but you will not have transferred this knowledge from your brain to your fingertips - programming is not a 'observer sport.' Just like any form of athletics, you have to practise a lot.
He's so right. I always try to write and run samples from books I'm learning from, even if I'm just copying the programs right out of the book. For most languages, there is a certain amount of muscle memory that your fingers will need to get; finding the '$' for PHP, for instance. But even beyond that, learning the keywords, control structures, indentation, etc is always easier when you are writing it, than if you're just reading it.
On a completely unrelated topic, but pointing to the same web site, I really like the direction the Programmatic Programmers are taking in the programming publishing field. I bought the Programming Ruby book and the PDF from them, and have used both, most recently using the PDF more than the book. If I like this Erlang book, which I can download preview chapters for, I'll probably just buy the PDF version and not the dead tree version. The price is right. And no dumb DRM in the PDF either; for instance, I copy/pasted the section above right from the PDF. I did have to fix the quotes and dash characters though.