I like to call them "I go, You Go". However, i have never done them with pull ups. I usually use that technique at the end of a bicep routine to finish them off. You get an insane pump and the bis are ripped for days.
I've never worked out with a partner, but I'd like to try it for a while just to see. I could emulate it by myself, but that doesn't have the same motivation as having a person there competing with you.