[jjjeffrey]

If a spacecraft were to travel orthogonal to the plane on which planets orbit the sun, would it experience the heliosheath as it exits the solar system? For that matter, have there been any spacecraft launched that didn't travel on the orbital plane (ignoring earth-orbiting spacecraft)?

[rohansingh]

Yes, it would. The heliosphere is not spherical, but the solar wind exists in all directions. The orbital plane is due to conservation of angular momentum, a completely different phenomenon.

[kryptiskt]

Ulysses (http://en.wikipedia.org/wiki/Ulysses_(spacecraft)) was sent into a polar orbit around the sun.

[youngerdryas]

Voyager 1 is at an ecliptic latitude of 34.9°, according to Wikipedia, so it is about 5.7 billion miles above the ecliptic.

http://en.wikipedia.org/wiki/File:Ecliptic_grid_globe.png

Edit: Whoops 5.7 not 7.5