Wired has a story http://blog.wired.com/monkeybites/2007/11/os-x-finder-bug.html on a bug in Finder (since 10.3 it seems) that may be of concern: "The issue revolves around moving data from one drive to another. If there's a connection problem during the move, your data won't be transferred (as you would expect), but worse, OS X will go ahead and delete the original data as if the move had been successful." Looks like the bug affects only file-moving, not copying.