I've hit the far side of the halfway mark in SWTOR, and though I've been lugging Khem Val for most of that (complaining every step of the way), I've yet to be asked to go on any quests for him.
I'm at 2500 / 10000 affection currently.
What affection levels does it take to unlock companion quests? Do you also have to be advanced to a certain part of the main story?