As of right now, I'm a dancer (ballet, jazz, hip hop, contortion, aerialist). I'm rehearsing for a show at my aerial studio right now, where we've got this huge "bird cage" that we get to climb around in and stuff, and I can honestly say that doing all the rail work and stuff for parkour has helped me come up with new ideas for choreography in our contraption, and has helped me with flow working in it.
As far as future careers, I would really love to become a stuntman (I guess technically I'd be a stunt-woman. lol) in which case I'm sure I'd use parkour a lot.
Another career I've been considering was to get a fire science degree and become a firefighter (I could use parkour to get in and out of burning buildings and save lives, how epic would that be?!?!)