My 73 year old grandmother friended me on Facebook last month. I have to admit, I was mildly horrified...mostly because I had to tweak a couple things to make my page Grandma-friendly before I friended her back. For instance, I immediately removed "agnostic" from my religious views...my ambivelnt views on Christianity is an argum...errr, conversation I really would prefer to avoid ever having with her.
I don't think she's visiting the site too often, though. Aside from a couple comments she received from a few other people right after she friended them, her page is mostly untouched and she never even finished completely filling out her profile.