M.J.
I have a 10 year old daughter & an almost 12 year old son. Neither of them has a facebook account, or even their own email address. Neither of them has a cell phone, either. Recently my son has been asking for a cell phone & I've made it very clear to both of them that they are allowed to have a cell phone just as soon as they are old enough to work a regular part-time job (jr. or sr. year of high school) & pay for one. I feel like that's fair because by the time that rolls around they will be responsible enough to handle it. They are given no time frame for email or networking websites, mostly because they haven't asked, but even if they did, I may just go with the whole, "Because I said so" line.
My husband is a Sheriff's Deputy & works full-time in a middle school. We are well aware what kids are doing, how they are acting, & the way they think. For all of those reasons & then some, I believe no kids need networking sites. They're kids! What in the world would they need to network for? If either of my kids wants to talk to one of their friends or their aunt or grandmother, they can pick up the phone & call any of them.