Even if twitter fails, you will still have a a network of people/friends/contacts and experience that will be invaluable to you. Even at employee #25+, given a

Even if twitter fails, you will still have a a network of people/friends/contacts and experience that will be invaluable to you. Even at employee #25+, given a significant rise in twitters value, you will still do well (e.g. the first employees at other services such as Amazon/Ebay/Paypal/other, which engaged in alternate or disruptive technology in thier time, did very well). Beside all that, it is much more fun to do things that can fail and walk a differnt path.