Porcupine Tree is is obviously a place where Porcupine's live, like you said, Faraday. Anyways, as a child, he lived in the mountains and had lots of land to play on and whatever the fuck, so he'd climb tree's or whatever, and find porcupines sometimes. He was even poked by a Porcupine several times. Being that he was amused by his childhood discoveries, Porcupine Tree is just a name with alot of personal significance to him. Steven Wilson has actually said this in interviews, so completely disregard anyone who says he won't tell anyone why.
Now that you know,you must leave and never return