I'm new to this forum and I've enjoyed reading this thread over the last couple of days. I've checked out Carl's guides several times, but had never taken a look at the forums until now, and I'm so glad I did! I loved the forums on the Sims 2 website, but have found the one on the Sims 3 website to be disappointing, so I haven't posted at all the whole time I've been playing the game, and I've missed discussing it with other players!
I'm an equestrian in real life (have been since I was a little kid), so obviously I was thrilled when Pets came out and we could have sim horses! As someone mentioned earlier in thread, I do wish there was dressage, as that is my discipline! I've had so much fun building horse farms, breeding, competing, etc, but there are still things I haven't tried yet, like adopting a wild horse.
One thing I've really enjoyed is having my sim work with "project horses" as this was something I did with my riding instructor when I was growing up. My trainer would purchase a horse who needed re-training (sometimes ones who had been mistreated, some who hadn't been correctly trained in the first place), and rehabilitate them before finding them new owners. To translate that to the game, I have my sim start out with modest funds and a relatively small lot with only one stall. I have the sim adopt a horse from a shelter, train it, and eventually sell it. As the sim's skills increase and she sells more horses, she's able to get better and better horses, and expand/move to a larger farm (I usually switch over to buying horses from the equestrian center once she has some money, starting with the cheapest and working my way up), until she eventually has a really nice horse who she competes until they are a champion, and then breeds. I play with aging on and have my sim have one child who eventually takes over the farm (I like the multi-generation aspect of the game). I just started a new family and I'm working on a new strategy that I'll post about once I've gotten a little farther.
Sorry for such a long post, I'm just so excited to have found a place to talk about horses in the sims!