Lizzie: Eats, Shoots and Leaves is, IMO, a brilliant book, both highly entertaining and informative. Although Ms Truss may appear overly concerned with punctuation--as any serious writer should be; it's there for a reason--she's really a pragmatist discussing punctuation for the same reason we're discussing grammar in this thread: because awkward or improper usage confuses or distracts rather than clarifies. Her advice includes a healthy dose of irreverence toward punctuation rules; ultimately, her concern is clarity, not fastidiousness.

The more attention a writer pays to crafting his language, the less noticeable the effort should appear in the end result: attention should flow unencumbered to the sense and the manner of expression, not to jarring side issues. Nor should the reader or listener need to mentally back up to puzzle out the meaning. There's a difference between idiomatic usage (which aids in creating character and place) and bad grammar (which just throws you like a rodeo bull).

I must agree with Truss: the modern habit of dispensing with punctuation hinders rather than aids communication. Out of respect for your audience, you shouldn't omit punctuation--or capitalization--any more than you should speak in a monotone. Punctuation is the written counterpart of inflection; use it well.