The res argument in the http.get() callback is not the body, but rather an http.ClientResponse object. You need to assemble the body:
var url = 'http://graph.facebook.com/517267866/?fields=picture';
http.get(url, function(res){
var body = '';
res.on('data', function(chunk){
body += chunk;
});
res.on('end', function(){
var fbResponse = JSON.parse(body);
console.log("Got a response: ", fbResponse.picture);
});
}).on('error', function(e){
console.log("Got an error: ", e);
});