Friend Request Ettiquette

Ok, so I'm new to this whole facebook thing. I recently joined facebook only because I had to in order to see someone else's facebook page and they spammed me with an email asking me to look check it out. Shortly after that, a couple of my actual friends who I didn't know used facebook "friended" me (stupid pseudo-verb, by the way) and voila! I was sucked in and I'm now one of the nine bajillion people who have a facebook page with an entertaining assortment of useless crap on it.

Soon after that, I was choosing musical artists I like, taking movie trivia quizzes, basically wasting a lot of time. I even apparently breached facebook ettiquette (or at least actual friend etiquette) by "poke"-ing Toast's wife, inadvertently thinking this was how you made her a friend so she could see the pointless crap on my particular facebook page. Toast and I dueled with swords and seconds at dawn and moved on with our lives. By the way, I later looked up the real meaning of "poke" and it turns out it doesn't have one - you cheeky facebook bastards...

Anyway, this brings me to friend requests. I recently got one from a woman whom I have never met. She is apparently a "facebook friend" of one of my actual friends. What's the ettiquette here? I've learned that I probably shouldn't "poke" her. She's a married woman. But, I don't know her. Am I obligated to accept such a request? My instincts say I should tell her to piss off. Is that a gross facebook violation? Is the point of this exercise racing to have the most friends? If so, maybe I'm not cut out for this facebook thing after all. What say you?