DOES NOT WORK ON SNOW LEOPARD!
From the developer's web site:
"I'm sorry to announce that, due to a OS bug, Startrail does not work on Snow Leopard. To be a little more specific, there is a certain case in which apps stop receiving mouse movements (if you want me to be more technical, please email me). Obviously this is the case for Startrail. I filed the bug to Apple, but since it is a very specific bug, I don't know when or wether it will be fixed. I'm very sorry, I tried some workaround but none of them seems to work. So please be advised that if you intend to upgrade to Snow Leopard, Startrail will not work anymore.
If you bought a license for Startrail after Snow Leopard release, please email me for a refund."