snooty posted some new previews! Below each link I'll try to summarise the new stuff mentioned, for those who don't want to read for themselves
http://www.simsnetwork.com/news/2011/8/21/preview-the-sims-3-pets-pcHorses are fully customizable: different mane types, short/long necks, fat belly, patterned coats.
New sim traits: dog/cat/horse/animal lover, no hater traits.
No pet careers on computers (console only).
Pets can only die from old age. No pet-related deaths for sims.
Minor pets include: turtles, lizards, birds, rodents, snakes, guinea pigs, baby squirrels. No rabbits for some reason.
Dog traits include: adventurous, aggressive, pig, friendly, genius, hyperactive, hunter, noisy, neat, calm, loves swimming, shy, snob, loyal, independent, playful, afraid of water, destructive, easily afraid (note that these are translated from german so may be worded differently in english games)
All pets can drink from lakes/rivers, but only dogs can swim in them.
Cat/dogs can use taxis, but not horses (duh). You can take dogs for walks, or ride horses around.
New community lots in Appaloosa Plains include: cat jungle gym, dog park, horse ranch (practice riding, jumping and racing skills - more below).
You can create your own race course, and can include fireworks (sims can burn their behinds). There are competitions and you can win cash prizes, trophies and a mention in the newspaper. You can also breed horses and buy/sell horses.
Sim homes can include horse barns with stalls for horses to eat/sleep/drink/woohoo in.
Dogs can learn tricks and the hunting skill, cats only have the hunting skill. Sims and dogs can enter trick competitions and win money.
Unicorns have two sides - sweet and angelic, and black and evil! They can start fires and drive sims out of town, and curse sims, bless sims, let plants grow where they go, and teleport.
A new lifetime wish is to add a unicorn to the household.
Children and below cannot ride horses.
...thats the first link. I'll get on to the next one