We've grown accustomed to seeing apostrophes inserted where they don't belong (as in, "I took some photo's when I was traveling in the mountain's") and omitted where they should be (as in, "Mens Room" and "Joes Bar and Grill").  We aren't cheered by this evidence that most graduates of American high schools have not grasped the one grammatical case in which nouns change their forms according to function in the sentence.  However, the malaise seems to be spreading faster than we can adapt to such slovenly usage and has infected contractions as well.  We now have such abominations as "Lets look at the evidence," "Whats the reason for this," "Heres an example," and "Wheres the party?" (or, worse yet, "Wheres the party at?" – another matter altogether).  Let's be perfectly clear about it:  The contraction for "Let us" is Let's, and lets is a verb, as in, "She lets her cat out every night."  As for Whats, Heres, and Wheres, there are no such words.  And that's (not thats) the truth.  Incidentally, as an instructor of composition, I have found a strong positive correlation between students' ability to use apostrophes correctly and their ability to think logically and write clearly.  Conversely, those who cannot grasp the simple logic of possessive nouns (and contractions) tend to be, to put it in politically correct language, logic-deprived. 

Those who wish to become enlightened about possessive forms of nouns may want to consult the article concerning possessive nouns in the "Writers' Guide."