ZaftigKnitting

I forgot to mention this the other day, but it’s an issue that comes up frequently at the yarn shop.
Sock needles will almost always end up curved a bit. Most wooden, bamboo, and metal needles (and other natural materials) will, with the pressure, moisture, and warmth from your hands, curve a bit. This is absolutely fine and nothing to worry about. It just means they’ve become “real,” sort of like the Velveteen Rabbit.
Certain materials won’t bend much (if at all): Carbon fiber needles (like those ProgrammerAtArms mentioned in his comment yesteray), laminated hardwood needles, and glass needles are unlikely to ever curve at all. That’s because they are made from bend-resistant materials, not because they’re better.
I, personally, LOVE a really curved DPN. It feels personal and loved!