Blind friend request on orkut and facebook

Hi friend's its long since the last post on blog.
Today I am to write about friend request received on orkut and facebook.
It's been long I am receiving friend request's from strangers or from fake profiles on orkut and facebook to approve.
I don't have any idea why am I receiving so many friend request?
Possible reasons:-
1)These people's are new to orkut and they want to add friend's in their friend list.
2)Friend suggestion by orkut/faecbook- If we have a mutual friend then they might be having me as a suggestion for friend request and they sent me friend request.
3)Even if these people are old to orkut, still they want to expand their friend list.
4)They know me through any forum or any other post in any community.
5)Might be, only they know me and want to add me as a friend.
6)Or their are no friend request, it is just an illusion of my mind i.e I'd gone mental.
Once I'd accepted around 10 unknown friend request and also I tried to connect with them but they didn't reply or on time.
And while I see friend request I asked to everyone-
"o you know me?"
or
"Do I know you?"
But there was no reply from the other side. Some of them chatted for a while and after some time they wander leaving me with no idea whether to accept their friend request or reject and accepting such friend request is a matter of privacy.
Many a times it is hard to decide whether the friend request is genuine or not? and in doing so it takes time which delay in accepting friend requests.
I could have blocked it, but most of my friend's don't have my e-mail address to connect with me or I need something else to make it.
Somebody please help.