iCloud set up SUCCESSFULLY in iCal (Snow Leopard 10.6.8)
I came across the 10.6: Add iCloud Calendar in iCal discussion, followed the instructions and successfully set up iCloud in Snow Leopard. I only tested one appointment but was able to create on iPhone then view using iCal and iCloud. Then I modified the same event using iCal and iCloud and all changes were updated correctly on all devices.
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MacBook, Mac OS X (10.6.8), White 2008