This has been my biggest struggle in the whole application process. I previously worked in undergraduate Admissions, and in some ways I think this gives me the tiniest bit of insight into the minds of a committee who will be reading and discussing applications. Conversely, it's made me incredibly nervous about making a bad impression on POI.
The faculty I've contacted have ranged from "helpful and nice" to "very curt" to "completely unresponsive." It's nerve-wracking, to say the least. Fortunately, I don't think there's a hard and fast rule. Sure, having a great rapport with a POI in advance of application reading is an excellent asset to your application; on the other hand, contacting someone who makes a snap judgement that they're not interested in you may defeat the purpose.
I think it's worth it to try to get in touch with POI, but I wouldn't force it. If you come off as awkward and unsure then you'll probably be perceived that way.