For all that’s good about Mac OS X and Apples legendary usability, it has the single most dangerous, stupid and braindead function of all operating systems, ever:
This happens when you drag a folder into another folder, which already contains a folder with that name.
If you are a Windows user, you know what happens next: The folder contents will be merged, which is usually what you expect.
What happens when you click "Replace" here? Well, Apple is at least honest, because it will do exactly what it says: It Replaces the folder. Your old folder is gone.
The braindead thing? The old folder doesn’t go into the Trash Can. If you delete a file in either Windows or Mac OS X, it goes into the trash can, so you can restore it. If you Replace a folder in Mac OS X Finder, the old folder is permanently gone.
With all due respect for the fine work the software engineers did in the past decade and a half: Whoever is responsible for thins function needs to be punched in the face, preferably once for every single folder that users – who are expecting a OS that values user friendliness to perform better – permanently lost.
What’s even worse: There isn’t even an option to merge. Really guys? "The world’s most advanced desktop operating system" does not even have a function to merge two folders through its primary file management tool?
(PS: For a similarly dangerous function, try moving a folder over the network and briefly interrupt the connection. Chances are good that the folder gets deleted from the source since it was moved, but doesn’t fully arrive at the destination because the connection got interrupted. Yes, the worlds most popular desktop UNIX fails miserably at basic network functionality.)
Update: Turns out that OS X Lion finally learned to merge, but only when copying stuff. If you are moving folders within the same Volume, move is the default. Holding down the option key allows you to merge:
This is arguably a lot better than any previous OS X Version. Still, it’s way inferior to Windows 95 which happily merges on move (saves me the cleanup afterwards) and can also merge a subfolder with it’s parent folder, something else OS X can’t do:
This isn’t needed that often, but useful when extracting a zip file yields a folder/folder/files structure.