I heard about this when it was still in development some time last semester, and I completely forgot about it until recently.  I finally downloaded it and started playing through it this past weekend, and I'm loving it so far.  I'm about 90-some stars in, so I've played most of the courses, and I'm amazed at the amount of detail and challenges worked into the maps.

You can download the patch at this site, there's a tutorial explaining how to patch it with the file, and the site also has some great 3D maps of the courses and strategies for collecting all of the coins.

I will warn you, it is INCREDIBLY HARD, at least for me, and it's often a bit difficult to work with keyboard controls.

Well, all of the levels were originally drawn up in Google Sketchup, then imported directly, so those maps were probably taken from the original .obj files.

But yeah, there're some interesting challenges.  Crazy wall-kicks, crazy Wing Cap maneuvers, and one course that gives you no hints to where the stars are at and contains exactly 100 coins (many of which are nigh-impossible to get on your first try).