Advanced Camera Orbit around target

Hi there!

I'm trying to figure out how I could make a mouse orbit script like they've done here: http://www.byggplanlegger.no/

This movement differs from the standard Mouse Orbit script in that the camera adjusts its position and rotation smoothly by rotating the local-y axis when scrolling directly over the poles, without suddenly flipping the vectors, turning the camera up-side down or clamping/locking the x-vector (up and down vector).

I've looked all over the unity forums for a solution with no luck.

Please help me in the right direction. Do I need to apply a matrix transformation of some kind or is there a simpler solution for this?

Thanks!