I traveled about 4 hours away for a wedding when I was 36 weeks (and my son was breech at the time). I brought a copy of my records with me just in case something happened.
I opted NOT to fly to my brother's wedding at 37 weeks (well, fly or a 13 hour drive) but probably would have IF DS hadn't been breech. I could live with going into labor in Random City, but I could NOT live with an emergency c/s in Random City.
I think the airlines get antsy if you're more than about 34 weeks - but a note from your care provider saying "she's not going to drop the kid on the plane" is usually sufficient for that. As for driving, I wouldn't want to spend more than about 4-5 hours in the care either way late in the pregnancy.