It is whatever you say it is
William Safire has now tackled the phrase it is what it is. (See a previous Capital Idea entry on the topic here.)
He calls it the tautology that it is (actually, he coins a new word -- tautophrase) and gives references to its use by Scott McClellan, Britney Spears, President Bush. A USA Today reporter named it sports cliche of the year in 2004.
And he makes the point that this is no phrase to get all huffy about: It's just an updated, less stuffy no comment for many. Some people employ it to express philosophical resignation over a disappointment, or so says the executive editor of the American Heritage Dictionary.
It is also used to get Eminem quotes stuck in Nicole's head: "I am whatever you say I am. If I wasn't, then why would I say I am?"
Que será, será.