That was fast, and highly unexpected! KSP 0.19 adds (according to the original forum post):
* Linux Support:
There is now a native Linux version of KSP! Official support for Ubuntu 12.04, but it should work on most distributions.

* Atmospheric Effects:
Watch your spacecraft flare up as they re-enter the atmosphere, and produce vapor trails during high-speed flight.

* New Kerbal Animations:
The Kerbals got a massive overhaul on their facial expressions! The new Expressions system uses the new Mecanim animation engine from Unity, giving Kerbals a lot more expressiveness. Watch their faces distort in total panic or gleeful joy, now also when you’re out on EVA.

* Rover Wheels:
Drive across the surface of other worlds with the new rover wheel parts, which are steerable and self-powered. Construct anything from tiny unmanned rovers, to exploration buggies, to huge mobile contraptions.

* Graphical and Scenery Improvements
We’ve got a New Launchpad model at KSC, with 100% less launch tower, a new Runway, and much improved night-time lighting, making for greatly improved visuals, especially at night.

* More New Parts
We’ve added several new parts for general construction. Featuring panels, girders, and a lot more!

______________________________________________________________________________________________________________________

I’ll be adding some screenshots in a follow-up post tomorrow!

Safe flying,
jiggyb2