In the US today, "hi there" is not often heard. The problem with it is that it has a frivolous, almost mocking tone, and so it is not usually used as a greeting. When greeting a friend, you'd say: "Hi," or "Hey." If you greeted a friend with "Hi there," it might be interpreted as you being in a bad mood, or you wanting to distance yourself from that person.
The experience of the Anonymous poster immediately above is not my experience. For me, it's more when you come across someone you didn't expect to meet. "Well, hi there!" might be said when you see someone in the grocery store you haven't seen in a while. I wouldn't infer someone greeting me with "Hi, there" was in a bad mood.