Very cool!  Apparently this was announced at the AGU meeting in December, but I missed it.

Voyager 1 is our spacecraft to leave the Solar System.  The “official” boundary is called the heliopause, which is where the effects of the Sun’s magnetic field no longer dominate the particles in space.  There’s a great (now outdated!) writeup here.  The heliopause has a long tail, so when you “officially” reach interstellar space depends on which direction you head out in;  Voyager 1 is headed out in the direction of the Sun’s motion, so it had one of the shortest possible trips.  

So we are now officially an interstellar species, with a spacecraft travelling among the stars.  Voyager 2 will follow in a few years.  The Pioneer spacecraft are on their way out, as well, but as far as I know we are no longer in contact with them, and I’m not sure which way they are going.  New Horizons (the Pluto mission) is on its way out as well.

Will humans ever lay eyes on these craft again?

[Clip from The Motionless Picture trimmed down to bare bearability.  For all of Star Trek’s corniness, ham acting, and bad physics, it has done a great job over the decades of popularizing interesting concepts in physics, astronomy, and space travel].

[Update: Stephen Kane points out an alternative (and better paced) fate, in this case for Pioneer 10:

Clip from Star Trek V: The Final Frontier (that’s the one where the Enterprise finds God at the center of the Galaxy and destroys him with a photon torpedo.  Can we please get an excuse to post a clip from an even numbered Trek film at some point here?!?)]