For me I think the LDR designation comes at around 2 hours of driving, or a flight. That makes it impossible to do just an evening "date" and it has to be weekends. The other problem is that with the amount of snow we get, in winter, a 2 hour drive can easily turn into a 4-6 hour drive without much warning. My current OSO is just over an hour away (this is tolerable), my previous one was in NYC and 4 hours away (that was too far for my tastes).
I have pretty much blocked off having LDRs, although it's possible that I may make an exception for someone that was really worth it. In general, though, I want relationships where we can be physically present in each other's lives on something more than a "vacation" basis.
I have met only a few poly folks who live a fair distance from me who, given other circumstances, I would maybe be interested in thinking about an LDR relationship with, but since I didn't get an overwhelming interest from their side, didn't pursue. LDRs miss so much of what I desire in a relationship.
"Listen, or your tongue will make you deaf." - Native American Proverb