I'm engaged to a wonderful man that I met in an online chat. We talked for a couple of years before meeting IRL, and have been together five and a half years now.
The biggest problem is the distance. I think that if you want a long-term relationship then you should stick to people in your own area. Phone bills and flights are too expensive so you should think long and hard about what would happen if you actually fell for someone before you start something with them.
Now we're faced with someone having to move to another continent so that we can be together. It's a tough situation to be in.
My best friend has met her boyfriends online for years, but she only talks to guys who live in our city. Most of her relationships were short lived, but she's independent so it worked for her.
Just evaluate what it is you want, and go into it with your eyes open. Be safe (that coming from someone who flew to northern Europe for three weeks to stay with someone I only knew from online).

<Yup, this is my first post. I'm a forum virgin here so be nice.>