Try hard. Play fair. Have fun. Respect your body. Honor your family. Thank your friends. Care for your planet. Breathe. Listen.
Proper use of punctuation is analogous to safety procedure used while climbing. It's all about details. Is this why I'm such a grammar snob? Not really, but I think it's a valid comparison. One who crosses his/her t's and dots his/her i's* would seem more likely to be vigilant of climbing safety habits. Indifference towards "your" and "you're" or "its" and "it's" could equate to disaster in a situation where gravity is playing for keeps. I appreciate proper use of punctuation because it demonstrates awareness and the desire to communicate effectively. I hold my climbing partners to similar standards: we check ourselves, our systems, and each other in order to "define" a safe outcome.
Here is a reference for proper use of the apostrophe: http://owl.english.purdue.edu/owl/resource/621/01/.
*This use of the apostrophe is not to imply possession, but to clarify. "Ts" and "is" wouldn't make much sense in print.