This is one of my favourite computing books.
After you've studied a couple 3GL system language's and played with Perl & scripting. Understand computing concepts, (Tcl probably isn't too good for random beginners or people who just don't like the paradigm). If you're into computing and want.., then go for this one.
When you are the only person on campus doing-knowing any Tcl / Tk, you had better get the right book.
I mailled Brent with a question and sure enough he got back to me. (try that with Lara Lemay).
So for such a good book and service - 5 star award.