I sent emails to all of my POI's (History), and got responses from almost all of them, including some really good advice in a couple of cases. My email was pretty straightforward like Anonymona's. I specifically asked if the professor if would be available to advise a student like me for the coming semester, and I'm glad I did because a few actually told me that they are retiring at the end of this year. I imagine you'd hate to go on and on in your statement of purpose about how Professor X is the reason you're applying to a school when he won't be teaching there, or anywhere, in 6 months.
Sending out a few letters to at least the professors who interest you most can save you a lot of headache.