My dad (58) just signed up and I got the friend request Sunday night. Right now, his friends list consist of him and some guy in his computer class, and me. But in a few days, I know I'll get a friend request from my mom and some of my aunts. I'm pretty sure this thing is still growing.
alas, for every person that delete their profiles there is another 2-3 that sign up. I am not saying that is sustainable, but they are growing. This is especially true in Asia where in the last 2 years has quadrupled.