When it comes to Social Networking sites, Facebook is the current undisputed king. When it comes to microblogging and 'status update', however, Twitter rules. Facebook knows this, which is why it offered US$500 million's worth of stock to Twitter, three weeks ago, to buy it. Fortunately, or unfortunately, depending on your perspective, Twitter rebuffed the offer. There were concerns that $500 million of Facebook stock wasn't actually worth $500 million, as well as worries over how Facebook would integrate the service into the site. Lastly, it seems that Twitter wants to have a go at seeing if it can make any actual revenue itself first, before letting someone else try. After all, despite having considerable outgoings in server, SMS and staff costs, Twitter doesn't actually make any money at all. Yet.