My thoughts:
1) The reason Tara did not match herself up against someone was to save her own behind. She was banking on losing a lot like usual (but waterlogging some to save up for next week), so even if Black lost, she was banking on them voting out Laura over her. However, she messed up on her waterlogging, not realizing how the luxury would affect her, resulting in a zero loss. She said she made one mistake. I think that mistake she meant was the waterlogging, not the overindulging.
2) If this show really wants to be about losing weight, then BL needs to do away w/ permanent teams for weigh-in purposes. Go ahead and divide them out for the trainers if they want, but they should randomly be divided into teams right before weigh-in and then go bakc to the 60 minutes between weigh-in and voting. That would virtually do away w/ the waterlogging and help minimize alliances some. Heck, if it were up to me, they would even break up who is with what trainer, especially after seeing the problems w/ the cousins this season. They could switch it up weekly or even more often. They also need to stop w/ the couples/friends/etc stuff and get back to picking individuals like in the beginning.