Not often used now, but they are plucked, cleaned and often dyed, then woven into baskets or as trim for clothing/hats. The guard hairs are also used for ceremonial head dresses.

So no, sadly, not a turn of phrase. I literally had my hands in a soapy bath of porcupine quills and shit, getting stabbed endlessly as I tried to clean them. I got maybe 40-50. They are in a jar to remind me of my folly.