It will always be worth it when you meet the right person. I know someone who met her now husband on a cruise.. they lived in different states and they made it work.
For two years in college I dated someone that was 9 hours away by bus / train / subway (we didn't have cars and public transportation isn't very efficient). It was worth it for us at the time and I have no regrets about it.
I've dated girls up to about 90 minutes away, much farther and I find that some tension builds up in the long run from travel time, travel expenses, especially depending on how busy the two individuals are.
I prefer to find a much closer girl, but will travel for the right one.