So, you can pretty much fly forever with a handy combination of the grapple while in the chute.
From pretty much anywhere, say, by shooting the grapple in front of you and slinging forward, you pop the parachute, push "S" (or back or whatever) to draw your legs up and gain a little lift, and right afterward, shoot the grapple at the ground again, followed by pulling legs back again. Repeat and you can maintain altitude at just about the length of the grapple, and if you aim it right, that height plus the height of the local trees, if you can hit them regularly. I actually scaled the mountain up to the casino and then scaled the casino itself.
Vehicles aren't exactly hard to come by, but if you don't want to backtrack to get a helicopter/plane, it sure beats driving a car. Seems faster and you're not limited by landscape.
This game is frigging awesome.