Node stealing is as rude as kill stealing. It's the equivalent of killing a mob someone else had already engaged and taking the loot. It seems like common courtesy but anyone who's ever worked in retail knows Hell is other people. They eliminated kill stealing in the game for a reason, which is the same reason they should eliminate node stealing. Maybe they could just change it so we harvest the node once and it drops the average mix of resources it drops after 3 harvests.
That said, I've only had people harvest the same node I'm on a few times. I say "hey! 
" they say they didn't see me and apologize and life goes on. It could be server culture. I imagine PVP and Exchange servers probably get a lot more cutthroat about everything, this included.
I've had someone take a node I was after but then I got aggroed. It's a little annoying but it's not nearly the same as harvesting a node I'm standing there picking away at.