One of the FAQ’s & concerns around the Sims community is the household limit with Pets. Today we have our answer confirmed via @BlackGarden who is hands on with Pets @Gamescom 2011.
The Sims 3 Pets Expansion has bumped the household limit by 2 totaling 10 members. This means you can mix and match between 8 Sims and 6 Pets that do not exceed 10. Pets will count as member of the household and take up a spot.
Note that only Playable Pets (Dogs, Horses & Cats) take up a spot in a household panel. Lizards, Birds and other collectible pets can be acquired by the dozens. (assuming you have enough money) Now this may not be the answer everyone wanted, but hey at least we have two extra spots to play with!