the AC actually doesn't use that many miles.... but the heat will use a lot. They recommend using heated seats in lue of cabin heat... luckily the winters here aren't too bad. And it still has a 200 mile range. I think they say you lose 5-10 miles of range per hr of heat...
I wouldn't take the tesla out for a road trip in the middle of winter, but i imagine if you were determined you could. They've got supercharger stations spread out every 100 miles or so, that take about an hour to give you a full charge.
I was able to drive from richmond to virginia beach which is about 105 miles with the AC full on and had 35 percent of batter remaining (50 miles). And i've learned of several tricks to increase range.
so i'd say you can reliably count on at least a 100 mile range worst case, which is enough to get to any supercharger station.
Tesla's are sweeeeeet.