I wouldn't get one if you're a first-time dog owner, or if you're not willing to put in some serious time exercising and training the dog. These guys are SUPER intelligent, but also can be very destructive. They're bred for working, so they need lots of activity (mental and physical) and can get destructive if they're not kept entertained somehow. They're also very loyal - bred to work with 1 cattleman on the range for long periods of time - and tend to be protective. They're fine with their family's kids, but you can't really trust them alone with other kids. I know a woman who breeds, trains, and shows them, and she's very picky (for liability reasons) about who she'll sell to.
Here's more info:
<a href="http://www.dogbreedinfo.com/australiancattledog.htm">
http://www.dogbreedinfo.com/australiancattledog.htm</a>
There are also a couple of good "breed selector" tools that can help you find the right dog based on your needs and preferences, as well as how much time you're willing to spend training a dog:
<a href="http://www.dogbreedinfo.com/search.htm">
http://www.dogbreedinfo.com/search.htm</a>
<a href="http://www.selectsmart.com/beta_dog/">
http://www.selectsmart.com/beta_dog/</a>
Good luck!