Truss' tongue-in-cheek style may not appeal to everyone and I don't agree with her about everything. In particular, "zero tolerance" makes punctuation an end in itself, rather than an aid to meaning, which seems back to front. It also makes no allowance for context and audience.
However, she gave punctuation and grammar a voice, and, however briefly, made people think about language, ambiguity and meaning, which is certainly good. Or it would be, if it didn't fuel the fire in the bellies of extreme prescriprivists.
A broader and more balanced book on this and related subjects is David Crystal's "The Fight for English How Language Pundits Ate, Shot, and Left" (http://www.goodreads.com/review/show/80173379).