I'm currently in a LDR with my poly partner. It worked well for a while as although the distance and travel-time was a pain in the bum, it felt healthy to have that time apart and look forward to seeing each other monthly. His other girlfriend was also a LDR for him.
However, she has recently moved in with him, and although it makes it easier for him to have time and money to travel to me more often, it's made it more difficult in terms of feeling stable in the relationship - feeling like we're all in the same position almost.
I think that LDR's can work really well where there is good communication and regular contact - emails/calls/texts whatever...and if nothing else, it's always nice to look forward to seeing someone you love.