Spanning Sync 3 is fully compatible with the to-be-released-Friday Mac OS X 10.6, a.k.a. Snow Leopard.
From SS Blog: “Spanning Sync 3 is fully compatible with Snow Leopard and takes full advantage of its support for 64-bit processing. (And for those of you with an eye for the technical details, the Spanning Sync pref pane is now garbage-collected.)”
Full details here.