Hmm, I have always included language summaries as a reference in my C, shell, and Objective-C books. Funny things is that I never get any sort of comments or acknowledgements about them, so I've come to assume they're not used or viewed as important by the users (they're typically not an insignificant amount of work to create---for example, there is not other Objective-C language summary that I'm aware of).
Many years ago I had done 8-1/2 x 11" plastic cheat sheets for Shell and C programming.
Let me ask your opinions: Would having it online (as it exists now) or even as a (free) iPhone app or ePub doc work as a quick reference or would you still like to see it physically in the back of the book?
Cheers,
Steve