Why don't Facebook and other major sites check the user agent and IP address of client as well, instead of just relying on a cookie? That would solve this problem in 99% of the cases, right?
Plus, your source IP can change from request to request when your ISP transparently pushes you through one of many proxy servers. AOL does (or did) this, as do some large European ISPs whose names escape me.
Are your neighbours on your private network? If not, you don't need to worry about them capturing your network data, because they're not on the same network.
