Mine lasted a year.

Me in DFW, her in STL. Luckily, that's a short flight, and thanks to the AA/WN wars at the time, a cheap one. We saw each other for a weekend every 2-3 weeks for the first 9 months or so, then both the frequency of visits and the strength of the relationship started to slip.

The way I saw it, we spent as much time together as most local dating couples. But instead of an evening together a few times a week, we'd have 48 or 72 hours continuously every 2-3 weeks.