A very good, and humorous, read on this subject.
http://www.amazon.com/Eats-Shoots-Leaves-Tolerance-Punctuation/dp/1592400876
From the description:
"A panda walked into a cafe. He ordered a sandwich, ate it, then pulled out a gun and shot the waiter. 'Why?' groaned the injured man. The panda shrugged, tossed him a badly punctuated wildlife manual and walked out. And sure enough, when the waiter consulted the book, he found an explanation. 'Panda,' ran the entry for his assailant. 'Large black and white mammal native to China. Eats, shoots and leaves.' We see signs in shops every day for "Banana's" and even "Gateaux's". Competition rules remind us: "The judges decision is final." Now, many punctuation guides already exist explaining the principles of the apostrophe; the comma; the semi-colon. These books do their job but somehow punctuation abuse does not diminish. Why? Because people who can't punctuate don't read those books! Of course they don't! They laugh at books like those! Eats, Shoots and Leaves adopts a more militant approach and attempts to recruit an army of punctuation vigilantes: send letters back with the punctuation corrected. Do not accept sloppy emails. Climb ladders at dead of night with a pot of paint to remove the redundant apostrophe in "Video's sold here".