I don't think that having a FB profile is important. I don't have one myself (for many reasons, privacy being the first one) but I see why so many people have one and I would never fault anyone for using FB. As for your second question, I think it really depends. If both of the candidates are "equal" in your mind (and I have to admit that I've never had that problem), FB can both help and harm. It all depends on who you are and what you have in there :).