Squad just released the latest version of Kerbal Space Program based on a Unity 4 build.

http://forum.kerbalspaceprogram.com/content.php/140-KSP-0-18-4-is-out!

==================================== v0.18.4 RC3

Bug Fixes and Tweaks:

* Fixed the latest version checking.
* Fixed some places that were using an old and inaccurate value for the vessel’s G-force, preventing entering warp sometimes.
* Fixed an issue which caused DAE model loading to fail.

==================================== v0.18.4 RC2

Bug Fixes and Tweaks:

* Fixed an issue where controls could become locked when switching focus out of a dead uncontrollable vessel.
* Fixed a collision issue with the large RCS Tank.
* Fixed a transparency issue with smoke FX and explosions.
* Boarding a vessel from EVA no longer toggles the SAS on the vessel.
* The VAB and SPH now show decoupler ejection forces on the part stats.
* Fixed a few typos on part descriptions and tutorials.
* Increased Jool’s rotating frame threshold altitude to prevent entering its atmosphere with the rotating frame disabled.
* Fixed an issue with the UI background not scaling correctly on the SPH.
* Fixed winglet colliders.
* Fixed EVA light orientations.
* Updated Copyright dates.
* Fixed vab transparency issue.
* Fixed Explosion Shader Transparency issues.
* Fixed Part Actions being clickable if Time Warp was engaged while the Action UI was already up.

==================================== v0.18.4 RC1

New:

* Ported the game over to Unity 4. Expect improved performance.
* Added a new stock spaceplane: The Ravenspear Mk4.

Bug Fixes and Tweaks:

* Fixed some buttons not being locked out properly on the Tracking Station and possibly other scenes.
* The Staging Stack now automatically scrolls back into view if a staging operation sends it off screen.
* Stage groups and icons now accurately follow the mouse when dragging.
* Fixed some UI controls and keys being responsive during pause.
* Fixed some sounds (mainly voices) being affected by 3D effects when they shouldn’t.
* Fixed an issue when going in and out of Map View after crashing the ship.
* Fixed the EVA map icons not showing.
* Fixed the planetary terrain not starting up properly sometimes.
* Fixed the error messages when exiting the game from the flight scene.
* Added a bad name filter for the Kerbal name generator.
* Fixed issues with the popup dialogs that allowed them to spawn a massive number of duplicates.
* Parts on the parts list no longer show the author on their tooltips (that broke immersion).
* Flight basics tutorial now requires player to set throttle to max before finishing the tutorial (and launching).
* fixed the non-persistent StateName field on MunFlight Tutorial.