(Reuters) - Facebook aims to connect all two billion Internet users. So far it has captured 845 million of them. Of the rest, nearly 60 percent live in Asia and hooking them is going to be a daunting challenge. A block on access in China, court cases in India and rivalry from other services elsewhere in the region stand between Mark Zuckerberg's Facebook and more than 700 million users. "The size of our user base and our users' level of engagement are critical to our success," Facebook said in its SEC filing for an initial public offering. ...