One of the most important factors is the ability to open one's thoughts and connect with the feelings of another. I think that is why the Internet can leave so many people vulnerable. However, those that are wise and can protect themselves against the idiots out there, can find many decent people online. Romance is something that definitely involves emotions. Between the ease that people feel not being face to face with someone, and the ability to say what comes to mind without having to look the other person in the eye, the Internet is a great tool for opening channels and making connections.
Disadvantages run deep on the Internet.
Another disadvantage is that the general population does not accept online romance it seems. Sure, it's OK to tell a co-worker or family member you met someone in town or on vacation. But, tell them you fell in love via the Internet and you can imagine the response. While it is my belief that one should live life for oneself and not get discouraged by what others think. However, it does add to the pressure when there are those attitudes to deal with.