Aussies are fantastic dogs, this is true. I'm also compltely biased.
HOWEVER--Twice a year they shed like it's going out style and have a little bit going on the rest of the time. If you don't like having to pick hair out of your food every so often, or like your carpets to stay the same shade without having to vaccum every day, don't get an Aussie.
If you can't dedicate at least 2 hours a day to training and exercise, don't get an Aussie. These dogs are active and smart as a whip and have no issue rearranging your house if they're bored. They are also very vocal dogs and aren't afraid to use their voices. You can teach them not to bark at everything and to stop when you ask them to, but just keep in mind that you cannot stop an Aussie from barking during playing. It's just how they are. Aussie get togethers are some of the loudest around.
They are the puppies from hell and it lasts on up until about 2 years of age.
Because they are herders, the first instinct will be to nip at your horses heels, not run beside them. Obviously with training they can learn what not to do, but just be warned.
Herding is something that takes much practice between you and the dog and sending an untrained dog on to cattle that aren't dog-broke is basically asking for your dog to get kicked or trampled. They have instinct, but it needs guidance.
Aussie Rescue would be a wonderful place to look for a dog around 3 years of age though. I got Sawyer through them when he was 18 months old and he's been the best dog ever. They are a fantastic rescue group and will help you figure out if Aussies are really right for you.