Ah. Sorry. I thought that was in this thread. Oh well - now it is. Thanks for bringing it up
Regarding your illustrations of zig-zagging pathes: Please don't confuse the actual followed path with the debug rendering (the one you're referring to) the debug rendering simply serves to show the order of the polygons in the path.
I do indeed plan to get a better NavMesh for the demo, but in this beta stage I've set that on low priority. This author is not a very good 3D artist, but I'm betting on that not being central in peoples decision of using the system or not.
Regarding the path following script and its abilities, I highly recommend you read the documentation at http://angryant.com/pathdoc.html and shift through the example code provided in the demo project (its not much).
I don't get which features you're missing from the pathfinding functionality and which you're requesting in a path following script. Currently the only parameter used aside from distance in pathfinding is the radius of the path finding agent. More are coming in 0.4b.