Looking into privacy features of social networking sites like Orkut , Facebook etc the feature I feel lacking is to hide particular scrap from all expect the sender or receiver.
They are having private messaging feature but it’s not catchy as the scrapbook,Introducing such feature will decrease little use of instants messengers over social networks.
Hiding a scrap from others will give great privacy , specially from those people who have habit of monitoring or peeping in scrapbooks.
In orkut locking a scrapbook is not so enough that friends can see all your scraps.