I've been following the RollerCoasterTycoon.com forums pretty closely through the open beta tests, and amidst a lot of complaining about bugs and the spline editor, JMR posted this video showing how he made hyper coasters into wild mouse style rides. I thought it was a good example of what could be done with the spline editor.
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Though I am glad about the announcement that they would be adding Piece-by-piece building, and generally working on making the coasters stable, I also really like the idea of the spline system! 
