I'm probably going to get significant disagreement with this one, but the more I play the more I am utterly convinced that Qum is irritating. The biggest point I noticed is, on one playthrough, entering the first Gathering with 89 (1 below the most important threshold) RP. And as such, she's really frustrating. "But... but Qum belongs to..." etc.
Let's put this in perspective. Your master, who you're mindlessly devoted to, is working on a plan to save the world and (as far as Qum knows) is currently suffering greatly for it. You have an opportunity to help him and your other hardworking allies by fucking some orcs or another succubus (as a species that craves and lives off of sex) and instead, you tell Yarra, your closest friend, to deal with it all herself. That's a shocking lack of commitment.
I'll also mention her "research," which asks Simon to take important resources from the previously mentioned world-saving journey to do nothing but create a drug that makes the afflicted follow her ridiculous speech patterns. How productive.
In addition, I haven't been able to get the vision out of my head of being in a life and death battle while Qum stands at the back occasionally casting buffing spells while exclaiming "Oh no! The Simon is getting his eyes gouged out!"