LSD FTW - or not...
I live with my wife N, and my girlfriend G is three timezones away. My other sweetie, K, couldn't deal with the whole ldr thing. I think G can deal better because she's more mature and has other boyfriends; I was K's first serious relationship in a long time, and we just couldn't make it survive the separation. I think it might have, if she had a local primary type relationship -- but the pain of having your only lover as a digital impressionist animation (yay videoconferencing) was just too much.
G and I try to do stuff together online. We'll watch the same shows on streaming video, or just work with the camera on and make faces at each other when the other isn't looking. Sure- sometimes I feel like I would cut a finger off for the chance to touch her for just a moment... but most of the time it helps us feel close.
And yes, planning for the €ŁĄ$ needed to see each-other is important. In an ldr your commitment and reliability count much more. But it can work.
In summary: (1) have local relationships; (2) hang out with each other online; (3) be seriously committed to maintaining the relationship and to meeting again, and reiterate this commitment often.