If you bought a decent machine that shipped with snow leopard I would recommend upgrading to Maverick. It's free via the app store, it sometimes requires reconfiguring startup patricians on machines that are 2 years old (I had to fiddle around with it to get it to install correctly). If you don't feel comfortable doing the install yourself you can always make an appointment at the genus bar and they'll install it for you. Just make sure to backup all your data. Maverick is faster for me, free, and was a small change on the front end.
If your computer is a few years older then I'd recommend either playing an older version of Aotbt or force installing it.