I haven't watched it yet, but apparently Arnie Shaprio actually has an opinion that matches mine--which he revealed on today's show--that Karen is the real snake in the grass on this show, and they've known this since they first cast her.
Based on how sneaky some of her actions can be, I agree. She has the girls totally trusting her. The guys, on the other hand, don't really see her as a threat. She and Will, as a team, were really on the warpath to get Marvin put up this week, but she also had the brains to know when to suggest Cowboy instead directly to Diane when she needed to. I also think that as much as the broadcast led us to believe that Will may be working on his own (with Jase), that he'd feel compelled to go back to Karen if it came to a reality and she'd pull some strings to her advantage.