Somewhere our brains lost track of not only the grammar rules but what looks correct. People have a tendency to throw apostrophes all over the place but the rules of useage are not hard.
Apostrophes are NEVER used to pluralize words; only, in fact, to replace a letter that has been omitted, as in a contraction like "doesn't", which omits the "o" in "not", or to show possession as in "Mary's dog", which expresses that they dog belongs to Mary. If you're not sure, figure out if you are talking about more than one thing or relating that object to something else. "The other CHAIRS are in the garage, but this CHAIR'S cushions need to be cleaned!"
There are some great tips that I refer to here at the Grammar Girl's website, and quite the funny picture description here: http://theoatmeal.com/comics/apostrophe