I know several LDRs that resulted in marriage, including one of my brothers who is now married with 3 kids. In all of these relationships, they generally saw each other every 4-6 weeks yet they were in communication daily. Perhaps most importantly, they weren't approaching the LDR as a "dating" relationship but as a conscious decision to see if there was marriage potential. If you approach a LDR as an expense instead of an opportunity, it's probably not for you.
I agree with Steve. I wouldn't write off LDRs. I suppose you just have to know when to take a chance, depending on what you are looking for and where you are in life. I personally wouldn't be willing to travel to meet someone that I wasn't genuinely intersted in for the long haul. If there wasn't a good chance that the relationship would lead to marriage, I would have to pass; it's just not practical. I am currently talking to someone who lives waaay up north. Normally I wouldn't consider it. However, he is an exception. I speak with him daily and he is planning on coming to visit soon.