Hey Guys, I know what you mean about the plug ins and junk.
I repair computers for a living and one of the top ways people get viruses is on Face book, My space, Friendster, when people using the apps, or applications. These are the "cutesy" games (but sometimes seem cool) that they offer like throwing water ballons, throwing pies, sending someone a Flaming Zombie Drink and so on...
The problem is, they are not from the website, they are from independent writers and many times viruses can be written into them, or because they are not written well, hackers can insert a virus in them. Also, as mentioned, they can be so poorly written they can cause system problems too.
I actually completely left facebook because of their privacy policy and security settings. If you look in depth and closely, they can use anything you put on the site, and in just about any way they want. You have to go in and set up your settings to NOT allow this to happen.
Not trying to be a know it all, but hopefully this might help those who didn't know about the apps and problems they can cause.