It's perfectly safe, and it's also easy to install -- as long as you're not using Facebook with "https". Go to TheKeesh, drag the image (or drag this text link, the image wouldn't work for me) provided on that site to your bookmarks bar, go to Facebook, and click on the bookmark you've installed.
Suddenly, you'll see a long list of people's names, each with a corresponding number. You'll notice that the names at the top are those whom you search and interact with most often. It's mildly shocking to see a list, right there in your face, of those you stalk the most. And no, I won't show you my list.
How is this list ordered? According to Jeremy, purveyor of TheKeesh and the guy who discovered this capability and created the JavaScript to view it, "I can only guess, but it seems like they order it based on who you interact with, whose profile you look at and who you have recently become friends with." He adds, "Basically, you will find a list which is mostly who Facebook thinks you are Facebook stalking."