Hi,
I know about long distance relationships. It is not for everybody. For it to be successful, the two people involved have to be honest and mature in the way they think.
This has its disavantages. As profitbob said, one of the parties could lie about things. Well to avoid this, after you have been talking on the phone or communicating via e-mail for a few months, both parties should make an effort to visit each one's place of residence, meet their friends and relatives to see what kind of person he or she is. Another thing to do is to do a research via internet the background check of the other person to see if he or she had some criminal record. You don't want to be dealing with an ex-convict.
Overall, on-line dating could be more expensive because both parties have to visit each other every so often.
Just like dating someone who lives closeby, on-line dating could also work out. I have seen friends who met this way and have successful marriages.