Even though I use a Mac, I don't install freeware, except from the Apple web site, or other trusted sources, like Adobe.
Mac OSX notifies you before it will download any executable, and asks whether you're sure you want to download it. You also have to enter the system administrator password to install it, even if you are logged on as the administrator. This prevents a lot of problems. It also requires you to give permission the first time a program runs, and requires you to give permission to get a password from the keychain (the storage area for passwords), the first time a program asks for it.
A lot of these are options on Microsoft, but apparantly it ships with all the doors unlocked, and you have to know how to change the settings.
I also turn off Java and Javascript if I'm going to a site I don't completely trust. Just a few things to keep the gremlins off the hard drive.
Agreed
These are things that I have been using for over a year and have had no trouble.
I just make sure they come from a reputable download site.